Have you tried thrift stores? I've gotten some terrific bowls (cheap!) that are great for snakes, with flat bottoms that won't tip. Not usually pet bowls, btw-
and I've been known to raid my own kitchen too, for a glass casserole or a vintage mint-green mixing bowl that my snakes are now enjoying. Just look thru
where they sell mis-matched dishes & baking dishes. Moving & Garage sales might also have suitable dishes, but I do far better in thrift stores because they
have a lot more stuff all in one place.

In past years I had some bowls, very heavy stoneware/ceramic that were made for pets...the kind that are sort of peanut-butter color on the outside, very
thick sides, and blue interiors (they were kinda pricey I think, & made in various sizes)...but honestly, I like my current glass bowls much better. One of my
snakes even has a very fancy salad bowl (make to look like expensive cut crystal) but I'm quite sure he's not impressed, lol. (it was only a buck or so)