Yeah, diff gears are the brain surgery of auto-repair. Alot of smaller "jack of all trades" shops won't touch them. Your best bet is probably to find a 4wd parts store and garage. They often service what they sell, and have a couple people on staff who are good with diffs.
Just know going into it that they may not just change a bearing, or may not offer warranty on their work if you insist that just the bearing gets changed. The shims wear down, and tolerances change as parts age. A new bearing may require additional work to get the alignment set right again.