You're there! The other Bonneville forum is www.bonnevilleattitude.com
Both of them are closely linked, and share common members. BA is more performance oriented, and less chatty.
As far as aftermarket parts go, the pickings are slim. Some of the drivetrain upgrades for the Grand Prix are interchangeable, but the GP never got the Series 1 L67 like you and I have, so there are gaps in the shopping list.
and domesticperformance.com are both members here, and support the Bonneville. The links section up at the top of this page will guide you to a few good sites, and the Techinfo section is loaded with good info.
Anything else you need, just ask! We can help with just about everything from part numbers for every stinking part on the car, to what kind of goop to put on your leather.
Welcome to the forum!