www.pplmotorhomes.com
The parts department will ship the fabric to you.
There are other vendors for the fabric including the awning manufacturer. If you do a Google search using RV awning fabric you'll see many listed.
I've had good service from PPL.
Also, most RV supply shops will order the fabric for you.
If you want to take a trip down to Chula Vista you can stay in the Chula Vista RV resort and there are a couple of awning installer trucks that cruise the resort. We had ours replaced last year. Reasonable price and good service.