While I was in the Ali distributors today, I asked about T Track & Sail track.
The bloke there showed me some 'Road Sign' track.
The book he had called it C Channel & it was about $15 a metre.
It was 25.4mm square & took a cup head bolt.... pity it is not quiet so deep 'cos once you route a 25.4mm deep groove in a 38mm top, there is only an half inch of MDF left.

I have attached a drawing I made when I got home.