They're so expensive!! How do I get them? Also extra question: Is it possible to know how many forum posts you have total?

You can get them from random events, piece 4 can also be won from Random. (the Game)

As for forum posts, you can hover over your username to see for quicker access.

Treasure Map Piece 1 also comes from Random, according to Subetalodge.

The price of Treasure Map Pieces has nothing to do with how actually rare they are to stumble across. I find over two months of doing quests that that's enough refreshing to either complete a Treasure Map or get spares of one of the pieces that can be sold to buy any of the nine pieces you are missing.

The price of these has very little to do with the rewards you get. You get five very rare items and a pittance in sP. Most of the rare items sell for Subeta's price-support price of 70KsP and only occasionally will you get a Potion worth a million or two. There's an Achievement for turning them in, and it has tiers. This is why they cost so much.

Don't forget map pieces are fairly new to being read and also I think is used in a Genentech combo for a minion.

Anything that can increase pet int in addition to being used for other things drives the price up

ohyeah that's so true! My readerpet hasn't even read them all yet.

INT boosters run around a million sP per point, so anybook cheaper than that is potentially worth at least that much..