I almost bought some Ballys in that color myself, but couldn't find the right style/size. (Only the loafers w/broguing fit me, and my fiancÃ©e voted against them.) I got some avocado trainers (with no belt to match) and some teal oxfords w/matching belt. Because the trainers are casual, I figured matching the belt wasn't an issue; my belt color depends on the rest of the outfit, or I sometimes just skip the belt altogether with jeans. (Wearing shirts untucked helps, too.) As for the oxfords, I did opt for the belt because 1) the shoes were dressier, and 2) they actually had one my size. (Plus, it was so cheap, it was almost free.)
However, I don't think I would always wear them together, as it's a marginally "fussy" look; I might wear a different belt with some ensembles. The mustard shoes should work great with any number of belt colors, especially browns/cognacs as well as oxbloods, depending mostly on what else you're wearing. Don't forget woven fabric belts"”you know, those hemp-like things. The combo should be very nice for summer wear. However, if you want a matching belt as one of your options, you could try getting a list of Bally outlets around the country, calling them and seeing if they have a belt that color in your size. Just because the outlet near you didn't have one doesn't mean the belt isn't out there to be had.