I have been getting the majority of my composite fabrics from these guys for years:
https://www.cstsales.com/
I like that they have a good selection, quality products, and that they allow you to buy in small quantities or save some money if you are willing to buy a decent size roll.
For peel ply specifically, I have tried all their peel ply and release layer products:
https://www.cstsales.com/a-vacuum-supplies-peel-plies.html
They are all good and give you some different options. I like the more porous release layers when I am doing vacuum layups because you get a more even coverage of the epoxy, but they leave a relatively rough surface that will need to be smoothed out (or not, the slightly rough surface could be a cool intended finish). The less or non porous peel plies and release layers leave a smoother finish, but you need to be more careful in your layups in order to ensure the epoxy doesn't pool up anywhere. Obviously, Mylar gives you a glass smooth finish, but is more difficult to use without pooling.
Their breathers are a good deal as well:
https://www.cstsales.com/a-vacuum-supplies-breathers.html
And, as a bonus, they are an Insta-cure CA dealer. Their prices are pretty much the same as most other places, but I figure I always need CA, so usually when I order composites I throw in a bottle or two of CA to get it all in on the same shipping bill.