Also, it wouldn't be cheap, but Hoosier R7's would be awesome. Even though they are DOT compliant.
http://hoosiertire.com/assets/circuit%20racing%2012%2020%2016b.pdf
Other DOT compliant R-compounds (for your application, stay away from autocross-specific compounds)
https://www.tirerack.com/tires/types/perfCat.jsp?perf=DRY
Wish I knew more traditional racing slick offerings for ya.
Since you're just playing around, if you found a local forum where people might sell their old race rubber, you could consider picking up a used set, for probably a small fraction than buying new. They wouldn't perform as good as new, but you're just playing around, used racing tires could totally fit the bill.
Clarifying your location (I've never heard of "RDU") could help us potentially suggest local options for you.