There has been a long ongoing discussion at G503.com concerning half-track tracks and having them reproduced. It now sounds like they have an European manufacturer for half-tracks.
BUT
It now sounds like there is an American manufacturer who is ALSO going to produce half-tracks...............and very possibly....maybe likely.....
Cletrac tracks..
I will provide more info as it comes available. Otherwise, you can go to G503.com, look under track section, discussion "Who can't find tracks".