You could just sign up for Kbin. It already lets you block instances from it's front end. I can't speak to the diversity of something like kbin.social in regards to US vs elsewhere though. Personally, I think a language filter would be nice. For example instances (or even community/magazine level) could have a default language property and you'd be allowed to filter on that. It'd be a shame to block an entire instance just because it's in a different country.
In regards to "US-specific" instances, I think the issue is more that folks in the US see less incentive to shoulder those costs if they can't sell it. The charitable bodies willing to do this or that I'd even trust to do it are few and far between. All of this is just a theory though. I have nothing but my gut feeling to back it up. So take it with a grain of salt.