Do you have a picture of the stuff in the room? That's a good place to start. Bring a drawer or something small to the store and compare it to the displays (they'll have the same stain on oak and pine so be sure that you look at the right side).
You'll also be able to tweak your final color with your finish. Waterbourne poly will give you a bluer tint, oil based will give you a warmer, yellow tint. If you need to darken it up a bit more, orange shellac will take care of that.
Then there's always ammonia fuming for a true mission look (depending upon what kind of oak it is), alcohol dyes, etc. etc. etc.
Post a picture of some of the existing furniture so we can see what you're trying to match.
p.s. You'll probably also be better off going to Rockler or Woodcraft for stain and advice. (Rockler's on the Rock Road in Bridgeton, Woodcraft is in Westport)