They use (at least) 12 (upgraded) SU-25s in Syria - a very similar plane with a similar mission to the (not upgraded A-10) - and, BTW, the Russians pioneered CAS in WWII with the Il-2 Sturmovik.
Russia’s A-10 Warthog: Why the Su-25 Frogfoot Is a Flying Tank
http://nationalinterest.org/feature/russias-10-warthog-why-the-su-25-frogfoot-flying-tank-17499
Sukhoi Su-25
https://en.wikipedia.org/wiki/Sukhoi_Su-25