Get 25% off all wet bags at SlingSisters.com right now. This Canadian company specializes in hand made baby carriers and quality accessories. You can find on their website pouch slings, wraps, pipa packs, reusable sandwich bags and wet bags. This is a really small company, but they might have the exact product you’re looking for, so I encourage you to have a look at their website.
This being said, I need to tell you that their website really needs some design improvement! Unfortunately when I had a look at it, the pictures and texts for the description of the products were hiding each other and their order form is everything but user friendly. Honestly it might take you a while to be able to understand it. But I still think we should give them a chance.