Which Atari? The 8-bit series: 400, 800, 600XL, 800XL, 130XE etc or the 16-bit ST series: 520, 1040, Mega, Falcon etc?
As an alternative to online stores, maybe you can find something on eBay, given that you find sellers willing to ship to Russia. There appears to be a great Atari community in Poland, so if you understand the language, perhaps Polish eBay could be a place to look. I even think one of the VCF members is from Poland.