Hi Chris,
As Tom said your head work will be done by your local automotive machine shop. Not knowing how hard the seats are in these heads, its best to just have them replaced with the other head work. New seats, valves, valve guides, and valve springs should be done. Have them lightly skim the head to make sure it is flat.
As far as suppliers go, the situation for us in the USA and Canada is very different than those in Europe. There are a few suppliers in the USA, but they are all very expensive. Mr. Fiat in Atlanta is a good source for maintenance items or parts you just have to get quickly, but big orders will be far less costly out of Europe, even with the shipping. I have found the UK suppliers are also too expensive compared to German, Dutch and Italian vendors. Many European suppliers and sellers will not ship to the USA, or if they do, do not know how to get reasonable shipping rates.
Biggest advantage you have right now is the Euro vs. the USD. The Euro is only about 12% more than the USD vs 30% more only a few years ago.
I have bought from various ebay sellers overseas and am in the process of making a huge order to some of the 500 European suppliers on the internet. I am going to post my recommendations and observations this week on this forum which should help you immensely. Hope you can wait!
John