I have used Delrin of the appropriate thickness and used the SS "track" clamped to Delrin "spacer" to pilot the holes. Both times that I needed to do this, "replacement" T Track holes did not line up and would have required filling and re-drilling. Using the existing holes, I rebed with Sikaflex 291, making sure that the through holes in the deck were properly sealed and then left a turn on the fasteners until the stuff cured. Then, went back and tightened them up.
Assuming that you are not in a remote
area, (Oh no mon, we got none a dat on de island, gonna take 2 weeks
) you should be able to find a local specialty plastics supplier to cut you the material of the proper thickness and width up to 8 feet long.
Just be sure that you de-burr and smooth the faces of the Delrin where the car slides on the track. A fresh smooth mill file should do the trick.