Where can I find Lego x-pod playoff pods for the game?
These are no longer in production, so your best bet to find the sets that you are looking for is Bricklink. Here's a list of all the X-Pod sets for sale.

These are the sets that were included in the game:


4348 Aero Pod
4347 Auto Pod
4346 Robo Pod
4349 Wild Pod


For building instructions, I'd recommend the instruction scans on Peeron. Take a look at the X-Pod theme there.

Here are the instructions for the game. See this question for more information on those.