I have a couple of these, threaded to suit my two lathes and I just swop over jaws and have therefore great versatility with only two Chuck bodies.
The last body I bought took ages to get, and the set of jaws didn’t really fit very well to both chucks.
The jaw holders are complex, if you see them you will know that a local blacksmith or even a CNC machinist would find them very difficult to make. All four are different too!
Sounds as though Toolpost are not able to supply, can they respond, please?
John