Ideally the material should be reinforced with a mesh.For whatever reason it seems rather difficult to source. A year or two ago I ended up purchasing from an e-bay vendor in the UK. Couldn’t find what I wanted anywhere else. It’s still available from them:
https://www.ebay.com/itm/313421676905?hash=item48f9634169:g:QhsAAOSwqTVgLBqM
I’m not sure what’s going on with the pfs-ware link that Buccaneer posted. I sent them a check earlier this year and my letter was returned as an invalid address.
