I havent been to UB, but tires in russia dont seem to be a problem. Yumax motors in Ekaterinburg had a good stock, and Misha & Katerina both speak english. In Vladivostok, Vladmoto has tires, Max speaks english (both places were real nice, & the folks very helpful) I also saw a shop in Tomsk with tires, but forget the name of it.
I put a set of Avon roadrunners on my bike before my RTW trip, and they lasted the whole way, 21k miles. This was on a heavy 1948 Indian. I didnt even have a flat!