Hi, I posted this on the MTB site as well, but my bike IS 1985 so I'm trying here too. Thanks for any help!

I have a 1985 Cannondale SM600 with 24" rear and 26" front wheels. I currently have black wall Kenda K Rad and Kross respectively, not aggressive treads. I want to switch to tan/gumwall. I could not find any back when I bought these and can't seem to find any now. Anyone have some ideas? Maybe I'm missing some source. Looking for not aggressive tread. Thanks!