China, for one. What's to stop them from buying AMD and reselling to Russia?

Though it will still increase cost to Russia with another middle man involved.

That is not without costs, in terms of both time and money. And I'm sure Russia doesn't particularly want to increase its dependency on China either.

They do want that. It’s part of their backup plan for being cut off from the West. That’s why Putin made a big show of meeting with Xi just before the invasion.

Not as a supplicant though.