Hoosier Race Tire Clearance
 

Lots of nonsense/ roundy round stuff/ gigantic Pro Street dumptruck tires, but there are a few Miata ish sized rains and slicks in there, too.

https://www.hoosiertire.com/discontinuedtires.htm

ii can nvr navigate there site ;(

On that page linked to hit "begin shopping". That takes you to the list of closeouts. Each closeout tire has a drop down list of sizes and pricing. Looks like the possible options in Miata-ish sizing are the assorted road racing radial slicks, ASA late model, and the road racing wets.

The ASA late model stuff is pretty tall for Miata, but the 23x9.5-15 Roadracing Slicks on 15x9 6ULs would be perfect. There were a few Rains that might fit weel, also.