As an update if anyone is looking for shelves. This place sells them in various sizes or to any size you specify. Their delivery times are a bit slow though. But I'm thinking it could be a lot cheaper to just get a piece of untreated pine cut at a diy place and buy some fixings!
Meadowland 20" x 10" KIln Dried Pine Shelf Ledge Chinchilla Degu Rat Guinea Pig | eBay