Off the top of my head ...
The front hubs are an odd size ... (74 mm?)
Some of the performance bikes have low spoke counts too so I suppose the the rims could be considered hard to get.
I forget what the seatpost diameter is ... perhaps something like 34 mm.
Some Dahon saddles/seatposts use a different mounting system. (IDG?) Although you can find those here and there on the internet.
-G