brotherstrucks.com is good but a little pricey
lmctruck.com is really good
classicparts.com has alot of stuff

Pick up the lastest issue of classic trucks and all the advertisers are in there, you can practically build a chevy or ford truck from a catalog.

1.Check your speedo cable to the tranny, probably bad.
2. Lights? You mean when you turn on the headlights the gauges don't light up? Could just need new bulbs for the gauge cluster. It's an 81 so your wiring should still be in decent shape.
3.Rattles could be cab bushings, just check them out from the underside and see what kind of shape they are in. The LMC truck catalog will help alot, every little piece of rubber you need even the ones you didn't know about are diagramed and available. Chances are most of the rubber is dried up and if you want to have a quiet ride you should just replace all of it. Not the cheapest route though.