Short answer: Pango
Use pango:⌘ instead of label:⌘. Pango uses fontconfig to find an appropriate font for each glyph.
convert -pointsize 128 pango:⌘ command.png

Explanation
Pango is a library for rendering text which ImageMagick can use. It has advantages and disadvantages compared to ImageMagick's label and -draw text. If a glyph does not exist in the chosen font, it will fallback to a different one. Pango uses fontconfig to choose an appropriate font.
Note that, instead of pasting in the desired glyph, one can specify the hexadecimal Unicode number using the $'\uXXXX' syntax available in Bash and other modern shells:
convert -pointsize 128 pango:$'\u2318' command.png
Fontconfig
Fontconfig can list which fonts can render a specific glyph by specifying a single Unicode character code as the character set:
$ fc-list :charset=2318 /usr/share/fonts/truetype/dejavu/DejaVuSerif-Bold.ttf: DejaVu Serif:style=Bold /home/b9/.local/share/fonts/DaxlinePro-Light.otf: DaxlinePro,DaxlinePro\-Light:style=Light,Regular /usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf: DejaVu Sans Mono:style=Book /usr/share/fonts/truetype/dejavu/DejaVuSansCondensed-Oblique.ttf: DejaVu Sans,DejaVu Sans Condensed:style=Condensed Oblique,Oblique /usr/share/fonts/truetype/dejavu/DejaVuSerifCondensed-BoldItalic.ttf: DejaVu Serif,DejaVu Serif Condensed:style=Condensed Bold Italic,Bold Italic /usr/share/fonts/truetype/dejavu/DejaVuSans.ttf: DejaVu Sans:style=Book /home/b9/.local/share/fonts/DaxlinePro-ExtraBold.otf: DaxlinePro,DaxlinePro\-ExtraBold:style=ExtraBold,Regular /home/b9/.local/share/fonts/DaxlinePro-Bold.otf: DaxlinePro,DaxlinePro\-Bold:style=Bold,Regular /usr/share/fonts/truetype/dejavu/DejaVuSerifCondensed.ttf: DejaVu Serif,DejaVu Serif Condensed:style=Condensed,Book /usr/share/fonts/truetype/dejavu/DejaVuSerifCondensed-Italic.ttf: DejaVu Serif,DejaVu Serif Condensed:style=Condensed Italic,Italic /home/b9/.local/share/fonts/DaxlinePro-Black.otf: DaxlinePro,DaxlinePro\-Black:style=Black,Regular /usr/share/fonts/truetype/dejavu/DejaVuSerif-BoldItalic.ttf: DejaVu Serif:style=Bold Italic /usr/share/fonts/truetype/dejavu/DejaVuSansMono-Oblique.ttf: DejaVu Sans Mono:style=Oblique /usr/share/fonts/truetype/dejavu/DejaVuSerifCondensed-Bold.ttf: DejaVu Serif,DejaVu Serif Condensed:style=Condensed Bold,Bold /usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf: DejaVu Sans:style=Bold /usr/share/fonts/truetype/dejavu/DejaVuSansMono-BoldOblique.ttf: DejaVu Sans Mono:style=Bold Oblique /usr/share/fonts/truetype/ancient-scripts/Symbola_hint.ttf: Symbola:style=Regular /usr/share/fonts/truetype/dejavu/DejaVuSansCondensed-BoldOblique.ttf: DejaVu Sans,DejaVu Sans Condensed:style=Condensed Bold Oblique,Bold Oblique /usr/share/fonts/truetype/dejavu/DejaVuSansCondensed.ttf: DejaVu Sans,DejaVu Sans Condensed:style=Condensed,Book /usr/share/fonts/truetype/freefont/FreeSerif.ttf: FreeSerif:style=Regular,нормален,normal,obyčejné,Mittel,µεσαία,Normaali,Normál,Normale,Gemiddeld,odmiana zwykła,Обычный,Normálne,ปกติ,menengah,прямій,Navadno,vidējs,normalusis,عادی,vừa,Arrunta,सामान्य /usr/share/fonts/opentype/freefont/FreeMono.otf: FreeMono:style=Regular,нормален,normal,obyčejné,Standard,µεσαία,Normaali,Normál,Normale,Standaard,Normalny,Обычный,Normálne,menengah,прямій,navadno,vidējs,normalusis,thường,Arrunta,सामान्य /usr/share/fonts/truetype/dejavu/DejaVuSansCondensed-Bold.ttf: DejaVu Sans,DejaVu Sans Condensed:style=Condensed Bold,Bold /usr/share/fonts/truetype/dejavu/DejaVuSansMono-Bold.ttf: DejaVu Sans Mono:style=Bold /usr/share/fonts/truetype/dejavu/DejaVuSans-Oblique.ttf: DejaVu Sans:style=Oblique /home/b9/.local/share/fonts/DaxlinePro-Regular.otf: DaxlinePro,DaxlinePro\-Regular:style=Regular /home/b9/.local/share/fonts/DaxlinePro-Thin.otf: DaxlinePro,DaxlinePro\-Thin:style=Thin,Regular /usr/share/fonts/truetype/dejavu/DejaVuSerif-Italic.ttf: DejaVu Serif:style=Italic /usr/share/fonts/opentype/freefont/FreeSerif.otf: FreeSerif:style=Regular,нормален,normal,obyčejné,Mittel,µεσαία,Normaali,Normál,Normale,Gemiddeld,odmiana zwykła,Обычный,Normálne,ปกติ,menengah,прямій,Navadno,vidējs,normalusis,عادی,vừa,Arrunta,सामान्य /home/b9/.local/share/fonts/DaxlinePro-Medium.otf: DaxlinePro,DaxlinePro\-Medium:style=Medium,Regular /usr/share/fonts/truetype/unifont/unifont.ttf: Unifont:style=Regular /usr/share/fonts/truetype/freefont/FreeMono.ttf: FreeMono:style=Regular,нормален,normal,obyčejné,Standard,µεσαία,Normaali,Normál,Normale,Standaard,Normalny,Обычный,Normálne,menengah,прямій,navadno,vidējs,normalusis,thường,Arrunta,सामान्य /usr/share/fonts/truetype/dejavu/DejaVuSerif.ttf: DejaVu Serif:style=Book /home/b9/.local/share/fonts/boecklinsuniverse/BoecklinsUniverse.ttf: Boecklins Universe:style=Regular /usr/share/fonts/truetype/dejavu/DejaVuSans-BoldOblique.ttf: DejaVu Sans:style=Bold Oblique
One could use that information to try various fonts with ImageMagick to see how they look. For example,
convert -font Unifont -pointsize 128 pango:⌘ command.png

Ugrep (name subject to change)
For convenience, you may wish to use a script I wrote called ugrep (name subject to change) that lists which installed fonts contain a specific character using -l:
$ ugrep -l command key ⌘ U+2318 PLACE OF INTEREST SIGN (command key) FreeMono Unifont Symbola FreeSerif DaxlinePro Boecklins Universe
Ugrep can also show a rendering of the character in each font, if your terminal supports sixel graphics, by using -Ln:
ugrep -L2 command key
