My recommendation was not exactly meant to mean do not mill the head flat. What I meant was don't just do it because you are doing the head gasket. A lot of people figure it is just a requirement, and shave off several thousandths just on principle. What you want is a flat surface, with as little lost metal as possible. If you just toss the old head back on without at least checking it, you are asking for problems, very true.
There are machine shops around now that are straightening heads rather than just milling them flat. They heat it up and apply pressure to one part or another in order to get it closer to flat. When they are done, you end up with little or no milling required.
I just meant to add a word of caution regarding cutting too much metal off and creating a new problem. LUVs seem to be rather sensitive to this sort of thing, from my experience. You definitely want to check for flat, and correct it if it is a problem when doing a head gasket. Just don't mill first and check later.
As for places to order from,
http://www.carparts.com or
http://www.rockauto.com seem to be fairly well stocked with LUV parts, though I do not know about shipment to the Great White North. Last head gasket I bought was from carparts.com and cost something like $20, tho it was just the gasket, no kit with the valve stem seals