I’ve occasionally seen reasonably priced and good quality girths in large sizes on eBay and other consignment sites, so it might be worth doing a search on there if you haven’t already tried.
It looks like the Bobby’s Signature Series girth is available in 58", though I will say that my 48" I bought used measures 51.5" from buckle to buckle (not sure exactly how much of that is due to stretching from use, but I also believe most of their tack runs large in general). It’s a soft and pliable girth, with pretty fancy stitching! The leather is not quite as luxurious as high end girths, but still nice in both appearance and feel, and the padding is thin, but squishy and comfortable.
Re: Voltaire, my experience is that those run a bit small, like you mentioned about European brands. While 4 of my 48" girths measure about 49.5" from buckle to buckle, my Voltaire Hunter Girth only measures 47". Looks like they go up to 62" from what I saw on their site, but doesn’t look like they have a 60".
Per non-leather options, the Classic Equine Soft Touch appears to be available in 58" as well. I have two of those in 48" and 52", and they seem to run pretty true to size. I’ve also had them for nearly 20 years now and they hold up well! They are also squishy and comfortable feeling.