Sorry, can't help you with what you're looking for, but check this out... the Veskimo comes with a hydration system as well!!!!! Look at "Drinking from the backpack" on the third page as you scroll down. Talk about best of both worlds...
If you can't find what you need, you may want to try this. I made one of these last month for my trip to california and it worked incredibly well for me. I tried finding some used panniers but finally broke down and purchased the aerostich. 1 gal Cooler I bought at Walmart for ~$5,.Freezer tubing at home depot for ~$3, and I reused a spare camelbak drink tube with mouth piece. Finally, I used a badge holder connected to my beanrider padded to snap the drink tube back in place. Really happy with the setup.
Ain't she beautiful! For 12 years Abby has been a faithful member of the family. Cushings disease however is taking a toll on her in her old age. We're cherishing every moment we have with her. Sorry to wake you up girl.
Note: forgot to attach the drink hose to badge holder in picture.