Hi Nick,

as far as I know they can not be purchased any more.
There was a guy in Gippsland custom making a similar unit, but he has stopped also.

I found some second hand units off old A class's after I had set up I beam on my new boom , so local boy's are using those .

I am using a short section of I beam, with roller car. A lot heavier, but it certainly works under load, mind you I am using 4 to 1 purchase on it .

Windslyce make a low profile recirculating ball car and track for outhaul similar to mainsheet track, that may also be a option.