Check eBay and try the factory. I was able to get a one page pdf on my 97 Sun Tracker Signature Party Barge from the factory Support line.
If you want it, I also have a pdf of the Sun Tracker Owners Manual. It's the 2005 rev but the factory support people said it is essentially the same manual they used back to 97. It's pretty generic to pontoons in general, but if you want a copy, send me your email in a private message.