Proxy merchants specialize in solving these problems. They are operating even now. Some of them exploit jurisdictional arbitrage (Bitrefill), some operate in illegality, but it always works.

One has something valuable (bitcoin) and wants to trade, there's a provider making sure this transaction happens for a fee (proxy merchants). How exactly they achieve depends on the exact conditions and environment. But it works...

Also, there are many people willing to buy bitcoin, so proxy merchants provide also the other side.