Sounds like your wheel drive belts are out of adjustment, and probably your right brake too.
On most WBs you can take out a pin at the handbrake, and loosen or tighten the connecting rod to adjust the tension on these. If this doesn't fix it, check the tension on the belt from the motor to the trans (under the frame). It should be REALLY tight in order to work well. If that's loose, that could very well be the problem with that.
As for adjusting the brakes, I'm not sure on a Lesco, but it should have a wingnut or just a nut that you can loosen or tighten to adjust them.
As well as your deck belt, if you haven't tried to tension it, try that. If you have tried that and you need a new belt, take it to your hardware store or I personally would go to Napa. Unless it is some really weird belt, a standard V-belt should suffice.