Cannondale T1000, Inbred SS 29er, Supercaliber 29er, Crescent Mark XX, Burley Rumba Tandem
The above is true, but I wouldn't want to count on the availability of exactly what I wanted. It's possibly you might find a 700c tire, for example, but then discover that it's actually too narrow fit safely on a wider 29er rim.
For this reason I've considered pre-wrapping and staging groups of parts to be expressed to me by someone back home in the event of a failure. For a 700c wheel, such a package might include: a backup tire, several spokes, in the various lengths needed, e.g. rear right-side, rear left-side, front wheel, etc. It also could include rimstrips, replacement loose or cartridge style bearings. Having such a box ready to go, with an address label that your supporter could fill in and drop off to you, could take a lot of stress and expense out of trying to work out a replacement, that could well turn out to be less than optimum for your needs.
Why not bring a spare tire, some spokes, an extra tube and some electrical/duct tape along - along with a spoke wrench, etc. When I was bicycling in the OZ outback I had extra spokes for my 48 spoke wheel and when the rear derailler smashed into the wheel a LBS respoked and trued the wheel in a "jiffy". Mind you I had to hitch-hike 700 km to get there. Getting the RD and other parts was the REAL reason why I hitch hiked.
It took 5 days to get a chain air mailed to me in the outback. Good thing it was just a spare - but not for long.
5 DAYS!!!!!!!! How long do you think it will take for the "box of parts" to reach you? If you are in the USA there are bike shops (and used bikes/wheels for parts) everywhere - well, almost.