the best i can figure out it is a High Tech Quick Relase Snap. mabey "Bull Snap" ?
i just did a web search for Bull Snap. there were several kinda like what you mighr want.
I M H O......that is not a reg sewing machine.... it was designed for Patch work.
For the same price you might find a consew 225 with a walking foot and be able to use 138 size thread For Chaps, for holsters check out the Cobra Machines,
sorry to hear about the black dye comming off..
This is what i do.
Dye with Fiebings Black Oil Dye 2-3 heavy coats.
let dry...... Buff untill no black dye comes off.
then FINISH WITH TANDYS SATEN SHEEN...........
a+ on you collar and a another A+ on you telling that they were perty much sewed on your Boss Sewing Machine.
for all that have had a Boss they need to take a good look at your work, and wished they
had it back.
i do know that the Larger Adler Machines have a sewing guide like you mention.
make contac with some of the sewing machine dealers that advertise here to see if they have what you are asking about.