I just ordered al the wiring for my rewire of a 22' 1976 Argosy. I had a few sources. Lewster, another member here, highly recommends Waytek.
They have great quality marine wire. I used 12/3 Marine wire for my AC side. I would have ordered through Waytek, but you need to get a minimum of 250'. I only needed 100' so I ordered mine on eBay instead.
I used 12 awg primary marine wire for the DC side instead of 12/2. That way I could color code each circuit for ease of identification. I ordered all of that wire from Tinned Marine Wire.
They have good prices and ship fast.
I hope that helps. If you have any other questions, I can try to help. Good luck!