[Mod Edit - Please dont link to sites which are known for posting exploits, encouraging other people to use them and getting people banned from the service - D]
Really? Most of those are when looking auction house “no auction to display” almost every wheelspin is as hard to get than taxi or crown victoria, you say hot wheels are rare ones but other forzathon shop car are easy to get, just like ferrari 812 right now there is zero 812 on sale. Or those reward cars when do something, like bmw m3 there is zero on sale right now. Pretty mutch only forza edition cars are really easy to get. One thing what that page is missing is po cars.
That you have most of them dont mean that those are more common like those you mention in op. And pretty mutch only really rare cars are those pre-order cars (and capri fe) and those are really hard to get, i have spent lots of time to try find PO 911 with no luck.
Also for consideration are the pre-order edition cars which are more upgradable than their counterparts:
2018 McLaren 720s PO
2018 Porsche 991.2 911 GT3RS PO
I’m going to drop the Ford Capri FE edition. Its the only rare car I don’t have (other than preorder stuff I don’t care about). I’m not even sure if you can get the Capri Fe at all??
The '04 is definitely in the regular wheelspins. Doesn’t come up often but I was one spot away from one this weekend. It does pop up in the auction house fairly often. I think I’ve won 3 from there. And at normal non-legendary price.