Just had a quick look on google & found a few references to the reservoirs, but the only sites I could find selling them were here in England (it was just a quick look though).
I have had good advice from Myatts in the past & you can view their price list in dollars.
http://www.myatt.co.uk/eup.htm
The listing is at the bottom of the page.
Reading about these devices on a thread on TubaNews.com, it seems that generally people prefer to wedge an absorbant cloth under the valves as all the water collected ends up in your lap as soon as you upend the instrument or lay it across your lap during rests!
Hope that's of some help.
Russ