Personally, I'd feel more comfortable buying a completely re-done head from the reputable source I posted, rather than trying to find new seats and bringing them to a shop who may or may not know what they're doing in terms of refurbishing. Cylinder head replacement can be done by any shop worth their salt, but not necessarily valve seat replacement - I'd rather not take the risk. Plus, I don't think $225 is an unreasonable price for a re-done head, and if you do the installation yourself, you'd be looking at under $300 shipped. And I have no idea where to source JUST the valve seats, to answer your question.
You'd have to find somewhere to ship to in the US though, if you go with the source I posted. They only ship to the US. I get parts shipped to Detroit and pick them up there.