Find someone locally who knows about tandems. Check on 48-spoke wheels.
Unfortunately single bikes can't take a tandem rear wheel. A primary source of the tandem's rear-wheel strength comes not from being beefier, but from having a greater spoke bracing angle, which requires that it be wider, which requires wider dropout spacing. While single road bikes' rear dropout spacing is 130mm (126mm in the 1980's when freewheels had a maximum of 6 to 7 cogs, and 120mm in the 1950's to 1970's when 5-speed was almost universal), tandems' is usually 145 or 160mm. They don't just put a longer axle and more spacers on it and use a standard hub shell, but instead, the tandem hub shell has the flanges farther apart. Santana takes advantage of a really wide spoke bracing angle and sells a pair of 16-spoke tandem wheels which have proven to be very durable and reliable.
The one or two bikes I'm aware of that Co-Motion made for very heavy people did in fact have the tandem dropout spacing.
Short of going that route, mountain bikes' rear dropout spacing is 135mm, which gives a bit of an advantage over road bikes' 130mm, and their spoke bracing angle is further improved by having the smaller diameter rim, 559mm BSD versus 622 for road bikes with 700c tires. And of course MTB's wheels are made a little beefier too.
All other variables being equal, adding spokes does of course help, but the last factor and by no means the least is the quality of the wheel build. Peter White at http://www.peterwhitecycles.com/wheels.asp
knows wheel building better than anyone else I know. I first heard of him through the tandem forum and the many, many members who had 36-spoke tandem wheels he had built for them that they had been extremely happy with. After having a lot of problems with a popular brand, I and my family have had Peter White build us several wheels, all of which have been totally trouble-free. Tell him you weigh 365 pounds by yourself, and you want to tour, and he will figure out a way to give you a good pair of wheels.
BTW, there are a lot of tandem teams on 23mm tires. We used 25's for awhile and didn't get any pinch flats (inflating to 10% above what's printed on the tire, as is customary for tandems and the dealer told us to do) but went to 28's for the less-harsh ride on our bad roads. We've tried 32's but I as the captain don't like the lack of side-to-side firmness.