Otherwise there's exchanges which still operate within Russia for the time being and some business (tho too rare to be useful but In a big city, if you don't have funds others than what was sent to you, you might be able to buy more than otherwise) accept it though I wouldn't rely on that too much unless you know a specific one.
However, not everyone can receive or send rubles as easily to/from the west especially after the SWIFT and related bans. Either way, it doesn't hurt to have the extra option.
Where might I find one of these (near mythical) beasts?
https://www.bitcoin.com/bitcoin-atm/
I've been seeing them occasionally in big cities since 2014-15 though again it's never worth it at least for me - the exchange rate is typically pretty bad and I'd rather wait but go through a low fee/feeless option.
At some point the flow does have to exit to something that a corporation or ministry controls; so an exchange business will necessarily appear, even if it's extremely high risk; someone will be in a position to pull strings. It's not a stretch when you look at how countries with weak local currencies have been operating for decades, just usually with USD as the preferred trade currency instead.