One problem you may run into as well is that most of the tubes available these days are valve off center. The CMPs, along with the M series deuces and dodges use valve on center. You will also want a re-enforced valve on center flap so the inner tube doesn't work it's way through the slot and blow.
The local tire shop here did the museums tires before I came, and they were using the valve off center and dragging the valves over. Some would fail in the first month, others worked until their first long drive. I think I have replaced almost all of them now, although they also welded the split rims on some of them to make them "safe", so most of those I have to scrap.
I bought some from Wallace Wade at the MVPA convention years back, and tracing backwards, later, from his part numbers I found the supplier in the US. They were happy to ship in quantity, and at favorable prices.
While they are made in China, they have worked out well for me. The part number for the 825/900R16LT tubes is 11021, and they have the TR440 valve. The flaps are part number 99012 and have the heavy re-enforced area around the stem. The distributor is Doberman.
http://www.dobermanntire.com/our_pro...17&subcatid=25
Regarding using them in a larger tire...my money says you would likely be OK. Are they for highway use or just casual use?