I gather that you want to treadle the machine rather than use the motor that is currently with the machine.
For the uniqueness of the spool pin and holder, probably not all that expensive. Those seem to get broken a lot. Ebay is probably where you will find it. Although, you might check with Helen Howes Sewing Machines. Treadle belts can be found on ebay, Amazon, Sew-Classic. Sewing Parts Online, Wawak Sewing Supplies, and many other places. You will probably want to look at post #12 of
My intro to the Treadle world and my love! (Willcox & Gibbs Chain Stitch!) to see how the ends were originally attached.
Looks like you missed
https://www.ebay.com/itm/Antique-Wil....m43663.l10137
If you hurry?? you may be able to get a new production spool pin
https://www.ebay.com/itm/New-Spool-P...4AAOSw1ZBUxdbN
Since I don't have a Willcox & Gibbs, I can't try on one, but I wonder if a thread stand could be used.
Janey - Neat people never make the exciting discoveries I do.