Get a new Vesrah head gasket kit, and everything you need will be included. It comes with a stock head gasket, which is all that is necessary for a stock rebuild. You should have the head checked for flatness, and milled down if necessary, but only as needed to bring it back to "flat". Copper head gaskets are nice, but not necessary. Get some new rings too. If the bores are in good shape, then you can likely go with standard rings.
Get intimate with Google, and find some vendors. You can start with Z1 Enterprises and Sirius.com, but there are LOADS more. Old Bike Barn has gotten some bad reviews here. You can find vendors on eBay, then go to their business websites to see what else they have too.
You sound like a newbie, so I'd like to know what you plan to do with the dremel. Are you planning to port the head? Those 400F heads are in pretty good shape to start with. If you aren't a master porter, then I recommend you don't touch those ports.
Camelman