When Shimano stopped making the XT thumbshifters I bought up as many pairs as I could find. Traded off the last pair this past summer. The only new quality alternative I'm aware of is to get a set of Shimano bar end shifters and install them on a set of Paul Components thumb shifter mounts. Silly expensive though.
Magura rim brakes, are you into trials?
This is most likely a long shot here, but if you have to have and can not find local, these guys stock it all,
http://www.bti-usa.com/public/index
They are wholesale only so you'll have to order through your local shop but they do ship international. These guys are friends of mine so yes, I am affiliated but have no commercial ties.
Good luck, and Happy Cycling (BOC
)
Bravo4