Nigel from Flashquark here!
I don't think we have any keycaps with Mac icons on them at this time, but we do have keycaps in general that you might be interested in: Flashquark.com
Aliexpress is good for clone caps. Clone caps are a bit of a touchy subject in the community, but if you realistically weren't going to drop $200+ on GMK caps anyway you can probably live with yourself. Drop also has a lot of sets in their MT3 profile, KBDFans has the PBTFans brand which has some cool sets. For other retailers that sell caps you have:
Cannon Keys
Divinikey
Kono Store
KPRepublic
Mekibo
Novelkeys
Vala Supply
Probably more I'm forgetting. For cheap sets that aren't specifically clones Amazon is probably easiest, but make sure to double check the layout compatibility.
kprepublic sent me a shipping notification with a fake tracking number (so I couldn't cancel my order anymore) and then waited until I emailed them to tell me the stuff I ordered was out of stock and wouldn't ship for 2-3 months. I ended up having to file a chargeback.
I've had better luck with KBDFans for cheapie keycaps.
As a fellow Mac user, I think you’re in for a challenge finding Mac media keys from anyone but Keychron, at least from my observations. Unfortunately most keycap sets don’t even include Command or Option keys. I own one Akko ASA profile set which does include those. I’ve also seen that PBTFans sets generally include Cmd/Opt, but I don’t personally own one. Best of luck!
Sorry I didn't see this sooner. I just did the same hunt, and came to the same conclusion.
I ended up getting the PBTfans Dolch set from Divinikey which comes with a decent number of relegendable caps: I figured that way if I missed them I could make my own media keys. But I'm getting along fine without them – I've been on the Mac long enough that I'm pretty well drilled on the ones I use.
Very happy both with the caps and with Divinikeys' service. I ordered a couple of other things from them – some new switches and a better switch puller – and both orders went smoothly.
I'm a little bit of an outlier because I pretty much only like uniform keycap profiles, but I've been really happy with my Akko doubleshot PBT keycaps. I'm using Akko ASA low profile keycaps on both my work and home boards and they're great. The profile is very similar to XDA.
Akko definitely makes some sets with mac mod keys, tho I think not all of them.
I just got mine off Amazon because I was lazy and wanted fast shipping. :P
For in-stock keycaps that aren't too expensive, try Cannonkeys, or Novelkeys when they have a sale. You can also check thocstock. Drop is also an option, although nobody likes Drop.
The coolest keycaps are generally sold as group buys run by dozens of different vendors around the globe. You can check mechgroupbuys or keycaplendar for info on those. (Or browse geekhack)