The covers were made in a few different styles by a few different company, but I don't think any of them were sold outside of the Japanese market. Naturally, there have been some imported over time and originals do pop up for sale on the Supra sites and places like eBay. There was someone who had a replica set (the one in that photo I posted is one of those replicas) produced as a part of a group buy I'm not sure who it was but it too may have been KevinM; He's on SupraMania and SupraForums and SM is where the group buy was hosted, IIRC.
Also of note, most will work with pre89 taillights, they fill the indented center piece; Takes mounting with a couple standoffs but may save you the expense of upgrading the tails. There were also some covers made for the pre89 lights, specifically. They're uncommon and I wouldn't count on finding set.
Pretty sure these are a DIY job:
These ones look good on a pre89... I think it would look best if you pulled out the yellow turn lens and tinted the reverse light a very light red.
This is a style someone suggested in that former group buy... never produced.
I have more of others but I'd probably spend the rest of my weekend looking for them, so "that's all folks!" (tm)