You can try outfittersupply.com for a breeching.
Years ago, I looked all over SE Texas for someone making a saddle breeching. Most saddle shops around here didn't even know what it was.lol
A friend of mines brother built me a real nice saddle scabbard. Nothing fancy but well made. I will give him a call this evening and see if he can make what you need. If he can, I will get you his number.
Thanks thats what i have been running into, i got a single copy of Mules and MOre magazine around here and am going to try to dig it up and call those peeps and see if somebody in Mule Country up there has one they can ship out, weird with all of the east texas mules there is not a mule tack shop anywhwre, at least i have never heard of it for sure, I used to order them from Leather Brothers along with scabards etc but not offered anymore, thanks for asking about the gun scbbard