It's on my bucket list to do one. I know some of the ins and outs from being involved with The Cleveland Youth Wind Symphonies when I was in college. (They go every other year)

How? Tour companies usually - honestly I would not do Europe on my own. Some of the same ones that do in the US will do international, but there are a few that are worth considering more for the international side. (If you do end up doing one, make sure you set up a site inspection tour in advance. They'll take you to travel the sites on a faster basis a year or so in advance in many cases) Often times they can help with equipment and such where you're performing.

For the districts allowing it? It's really a matter of getting your admin and school board behind it. I've had discussions with my superintendent about the possibility. She and I aren't convinced the town is quite ready for it. I've considered suggesting Toronto as a first dip into an international trip. Probably wouldn't be more cost wise than what we've done for NYC, Cleveland last year, or Florida that we're doing next year.

Of course, traveling internationally brings about headaches with passports and such, but it can be done.

Keep in mind every community is different. I've had friends who were in your situation, and some that were in even stricter. We're on a 2 year cycle with out of state trips where I'm at.