Dr. Pepper,
The Halacha regarding Heter Meah Rabbonim says it needs at least one rabbi from three countries. Most opinions say three different US States suffices for this purpose. If you want to be more careful you can get one rabbi from each Canada and Israel in addition to 98 Kollel yungerleit in Lakewood.
Yes, air travel in the past made it more difficult to procure. I don’t suppose anyone will insist sending a horse and buggy to Toronto (or to New York, if another State suffices) for the out of state/country signatures. Many things became “easier” in Yiddishkeit due to advanced technologies.
A HMR is not limited to the type of cases (and related thereof) that you mentioned. It is far more expansive to include any case where the husband has a reasonable reason to desire divorce whereas the wife is unreasonable in refusing.
As far as acceptable, the only person that will need to find the issued HMR acceptable is the one rabbi that will officiate for the husband’s future marriage. Anyone else’s opinion has no bearing. (Halachicly you don’t even need a rabbi to perform a marriage.)