Probably needs more than replacement parts. Water and a BB do not mix whatsoever. Plus you left it on/turned it on before it was fully dried out (takes 4 to 5 days in a bag of rice) which makes it worse.
My experience tells me that even if you manage to get the track ball and keypad working, you will end up with more problems making it not worth the investment. the best bet is to get a new device.
But if you insist, use Google to find the parts. eBay might also be a source. Here is a link to a repair center I found using Google Search. PDA Repair World – The World’s Best Provider of BlackBerry Repair Parts, BlackBerry Repair Services, & Accessories. BlackBerry LCDS, Track Pads, Touch Screens, Housings