It's probably because socket 1156 had a very short life span of just one year. Where are you looking btw? I can find several boards here in Denmark. Mostly H55 ones, but there are some P55 ones, too. Also some 3420/3450 Xeon boards.
It didn't circulate in the market too much. P55 chipsets weren't bought nearly as much in volume as X58 ones purely because it offered no real tangible benefits but a gimped chipset. That and people who found out about LGA1155 decided to wait. It's not a bad chipset, just that Intel screwed over the users because of the small scale of production with it.
