I’ve found sources that sell Piano books for Mother2 and Mother1+2 for relatively affordable prices…
I do have the Mother2 Piano book, ordered from the source below, it comes shrinkwrapped, and it shipped fast; I am happy with the book and the seller.
I do not have the Mother1+2 Piano book, and it’s from a different seller, so I’m not sure how good they are. I am going to buy the book soon when I get my allowance this month… maybe… unless something weird happens like a sudden release of a Mother1+2+3 compilation for the DS…
Anyways, here are the links…
Mother 2 Piano Book: http://www.otaku.com/cgi-bin/itemview.asp?itemid=75196a
Mother1+2 Piano Book: http://www.vgmworld.com/catalog/index.php?table=cocoebiz_sheet_music&item_num=5
These are going a lot cheaper than what I usually see go on eBay… and these are new. (The Mother2 one is, at least. Like I said, haven’t tried the other seller yet.)