Source for Large Food Safe Plastic Bags

I use large plastic bags to cover a 1/2 sheet pan when rising my bagels overnight in the refer using the bagel formula from Rinehard's "Crust and Crumb".   The supply of bags I am using now I acquired from my late mother-in-law about ten years ago and they are the right size and are sturdy enough for multiple re-use.  I am down to my last dozen bags and need a new source.  These bags are fairly heavy gauge plastic and large enough to fit easily over a 1/2 sheet pan with plenty of head room for dough to rise inside.  I have located a bakery supply company that sells similar sized bags on a roll of 500 or 1000 but the material is quite a bit thinner than what I have been using and are essentially one-use disposable bags.  Does anybody have a source for heavier weight plastic food safe bags in the size I am looking for?

Thanks and Happy Baking!