I think that these cast brass buckles are off of some part of horse tack. Does your buckle have an integrally cast stud in the center of the reverse side? I tried to Google around for a picture, but I am either too slow today, or I am not finding the right vocabulary for the search engine.
I have personally found identical buckles at TOC - mid 20th century sites, mostly in a rural context.
Hopefully someone smarter and better looking (is that possible?) than myself will come along and help you narrow it down a little more.