I got mine done by Peter Tan in HK.
Great service, very cheap - cost me around $240 (couple of years ago) for postage/insurance/replacement filter/labour. Can't recommend him highly enough.
You really may have to go O/S but it's not as much of a drama as one might imagine.
Good Luck
Doug
ps...contact Peter via his email link at the bottom of his web page:
http://www.tan14.com/gears.htm