The slide closure and quick-release drink tube look pretty similar to the Hydrapak bladders that come in Nathan packs, but might fit existing packs. They're available separately, as I assume these are also? Check the dimensions in your packs and you might not have to replace them.

My main issue with the Hydrapak quick-release is that it defaults closed on one side, I forget whether it's the bladder side or the drink tube side, but it means that you still have to pull it off if you want air to flow through the component for drying. Do you know whether these stay open when separated?