Pismo parts are very plentiful on the 'bay, you can find almost everything you need at a fairly reasonable price.

Tony ZZ on eBay (no relation) has fast shipping, good communication, fair prices. He also has a nice supply of batteries (original Apple ones) that he gives assessment of condition so you can price-match to what you need. I have had good luck with Apple batteries, many of them still hold a charge quite well. Expect to pay at least $30-35 for a battery with decent runtime.

Get that Pismo humming again! They are my daily workhorses, I started buying 'em about a year ago and couldn't stop.

Good luck!