Most parts on bikes are not brand specific. Head to a local bike shop and they can assist you with part selection. Yes, prices at shops are higher, but ordering stuff over the internet is best suited for someone who knows EXACTLY what they want.
As far as value, tandems have very little value. First, you need to find someone who wants one (small market). Secondly, the pair of riders need to match the size of your tandem (much smaller market). Third, shipping a tandem is very difficult, so you are left with the local market, which may be non-existent in your area (or could be strong). My area is the non-existent kind. I had two tandems, offered them at the price of just ONE tandem's crankset. No takers! I finally removed the cranksets and sold them both for over DOUBLE what I was asking.