I just got my brother The Settlers of Catan for Christmas and I noticed that the main game is only 3-4 players. I need an expansion pack to make it playable for up to six. Anyone have one available?

That'll be pretty tricky to find. I just bought the entire Catan Series a few weeks ago off Ebay for $118. (SoC, Seafarers, Cities/Knights and the 5+6 player expansions for each).

If that's all you want is the 5-6 player expansion for the original, then I might suggest just getting a 2nd copy off amazon for $15-20 shipped and just converting some from that set into different colors. It'd be cheaper and there are actually allot of maps that require 2 original sets.

Check that anime store in town. I forget what's it's called; it's on Pine. I know they have the original Settlers, I think they have the expansion.

He is thinking of Eclipse Games, and yes, they have the 5-6 player expansion available for the SoC stand-alone for around $20.
At least, it was there last time I was in there 2-3 weeks ago...