When you say you want the window tracks, do you mean the regulator assy, as in the crank & scissor type arms. Sorry, I don't know all the terms for these things.
On my 73, I noticed that the ones from a 76 door appeared to be the same except the rollers were a different size. I went to
www.chevyduty.com & ordered the rollers for the 67-72 & they were the same size.
If you need the window regulator out of a 76 door, I could probably help you out. Then you would just need to order the rollers, drill out the old ones, & fit the new ones on there.
Mike