If you can only get a hold of 1/8th foam tyres you should be able to cut a pair of rears to fit all four corners of a 1/10th buggy. As the previous poster says it would be advantagous to have access to a lathe (If you've never used a lathe best to get someone to operate it on your behalf though)
I used to race indoors on carpet in the 90's and I used 1/8 tyres. Never had a lathe back then so used to do it by hand and then after gluing, I would use a drill and sanding block to buff the tyres down a bit to a lower diameter (not essential but sometimes helps)...won a lot of races but these days I'm getting a bit old!!
I've actually just bought myself a set of 1/8th foams in the UK for my own 2wd as you do get some serious grip on smoother indoor (carpet) tracks!
Good luck buddy!
Jim