Good morning and Welcome Calvino, glad to see that you are looking for a collectable version of the Supra. I guess the most individual and factory affiliated model would be the TRD Supra's, these pop up now and again, but mostly are available via Import, although I think I am correct in saying, supply is becoming a lot more restricted as numbers in Japan reduce.
JM Imports recently imported TRD car No.7 (maybe 8), so perhaps give them a call.
If you are looking at factory build stock bodied rarity, then there are a few choice colours which are becoming harder to collect also, a few to mention are:
Royal Sapphire Pearl
Deep Jewel Green
Quicksilver (still rare, but not as rare, still a fantastic addition)
Yellow
Anthracite (MSB as its affectionately referred to )
Then you fall into body types, you get a Hardtop version which is most common, Aerotop which has a detachable roof section that fits into the boot. There are also Facelift and Pre-Facelift models which have varying differences.
There are a lot more differences which I am sure others will point out, I am not totally clued up on the rarity aspect, but there are others who are in the know.
Hope this helps