Birkenstock Montanas seem to be a bit difficult to find. Ebay and abroad are probably the best places to find them. Birkenstock USA currently doesn't stock them. They're something I've been on the lookout for due to their exclusivity. We're all egotistical fools and we might as well feed the beast.
The Montana has a hiking vibe that fewer are looking for these days. Look alike Alabama is an option but it isn't the same. That dull lacing system just doesn't do it for me. You wouldn't feed your child store brand Cheezits, would you?
Anyway, sort of a divergence here: I had a pair of knockoff Birkenstock clogs that I wore around my hometown. People perceived them as feminine and I took shit for them. When I wore them at boarding school, a good portion of guys wore them (and got in trouble for wearing them to class). While this occurance isn't unique by any means it's one that you have to keep in mind when meeting with unworldly folk. Your dub-monks just might be fruit boots to them. Unfortunate? Yes. A truth of life? Unfortunately. Just remember: if people have a problem with the way you present yourself "fuck off" seems to have worked well in the past.
-exception here would be to have clothing standards for work.