We are the ones doing a full rehab on a 2007b 19H now. I researched replacement canvases extensively and also had the following issues:
1) couldn't locate part #s
2) couldn't find used canvases
I decided to use Sherry at RV Workshop
https://www.rvworkshop.com/. She told me Jayco still makes the canvases and they ordered both factory direct for $920.00. They will be here in a few weeks. She also offered me free shipping if I paid by check. I couldn't find a dealer in my area who was willing to order the canvases for me... bizarre!
I can keep you posted on mine when they come in if you want!