It's called 'T molding' or 'Tee moulding' by Outwater Plastics where I bought it years ago. I believe what I bought was 3/4" teak wood grain:
https://www.outwater.com/products/zz-105-679/
I either bought 25 feet or I bought more and sold the rest on this site. I can't remember. The web site says it is only available in 250 ft coils. I would talk to them to see what kind of deal you can make with them. Other people on the list have gotten non-standard orders on extrusions from them.
The other useful product they have is sliding cabinet door track.