I am also in the middle of cooling sysetm up-grade and the type of hose that I have found best for the Pantera application is Gates Rubber Company product line: Green Stripe.
http://www.gates.com/index.cfm?location_id=1175 It is designed for heavy duty use and addresses cold weather sealing. (not a California issue)There are several types within the Green Stripe product line; 2 ply, 4 ply, Vibraflex and others. They also have sizes for the heater hoses.
I had orignally wanted to use silicon based hoses for appearance and easy removal for later disassembly but there are some disavantages with silicon.(perhaps there is input from others on silicon hose from the B.B.)
In terms of distributers you will have to do some searching So far I have found it is special order from an autoparts store once you find someone that knows what you are talking about. Be ready for the pricing it's premium hase and the price reflects that. $$$