Knitting Machine Parts

Yes. The makers of knitting machines have this experience.

The machine is vintage 1940's Protti made in Italy and noone I found has ever seen tensioners like it

Old Knitting Machines

A long shot suggestion would be to Google for old timers that repair sewing machines. It should be easier to find them and there might be enough overlap in the customers and manufacturers to yield something useful.

Last week I was talking to a guy that has been repairing sewing machines for 60 years. His business puts a lot of focus on old machines from Europe. The reason? They still work well and are made to be repairable. He gave me a "no bid" to service a 3 year old machine that is giving my wife trouble.

I know sewing and knitting are not the same thing but if you run out of good ideas this could be your "plan B".

Are you trying to "restore" the machine to its original state, or, just trying to get it to work.

If the former then you clearly need to do some research. But, if the latter then I think you would be better off retrofitting a modern feeder/tensioner.

The original was almost certainly an all mechanical design, which probably took an enormous effort to optimise. An electronic controller would be much easier to get working.