Hopefully this finds its way back to you and all I have spent two months trying to find something that works.
I found a double sided threaded stud that works for this... I cannot find the track or trollies to date.
But if its the black stud you need McMaster Carr sells something that works.
https://www.mcmaster.com/
Part number is 94455A325 Left hand to right hand thread adapter
1.58 Each
Hope this helps