I am very surprised to hear that authorized Mesa Factory Service shops are nonexistent outside of the United States. Regardless, Mesa repair parts will always be nonexistent to those who choose not to order them. Of course, there is no harm in asking around for direct replacements from local sources, however, when no clear options are found, as in this case, then I suggest going straight to the original builder. At the very least, contact Mesa before going to forums full of guys who aren't really sure and are only guessing. I don't know where Mesa sources all of their parts from, but if the situation that you describe is accurate, then it would be a reasonable assumption that Mesa would advise on how to purchase the part(s) directly from the original manufacturer or a local supplier. If that is not desirable to the customer, then Mesa does ship parts all over the planet. That's how their amps get there! I have ordered items directly from Mesa's Petaluma factory many times. The pricing may be a bit steep, but the parts are perfect replacements. 100%.
You know, not everyone is in the US. Mesa products and even spare parts have been non existing in Europe for the last couple of years.