the collars that you are reffering to would be of the "BDSM" variety? Assuming that is correct I have seen several of these around and would make you an instructable except that I do not have the materials nor a job to get them... (does anyone still have a job in the US anymore?????) However the basic concept is the same as that used to make homemade belts or any other form of homemade leather working.. You should just be able to look and see if there is an instructable already on here for homemade belt making or something to that effect and then just modify your sizes and dimension for the affected/afflicted neck. Another idea would be to google both homemade beltmaking as well as how to make authentic medieval costumes at home...... I know a lot of people who are big into Medieval reconstruction and almost everyone does their own leather working for their costumes/outfits (as the like to call them).