training pants

I've been looking for potty training pants for Oliver. I went to BabiesRus, Target and WalMart. Target had NOTHING. Walmart had them but not in any size under 24 months. Babies R Us had some in every size EXCEPT the size we needed. I didn't even see a spot for them! There were 12 months and 24 months but no 18 months. I've been looking online but everything is so expensive. Does anyone know about Potty Scotty training pants? They are affordable and they have some that are waterproof. I'd like to get some opinions before I buy them.