Do you already have the merchandise made, or are you looking for someone who will manufacture AND sell/distribute it for you? If you're looking for the second, there are certainly companies out there, cafeshops.com for example. Don't expect to make any money from them, however, because they tend to have high base charges for merch.
If you're having the merchandise made separately and just need a distributor, I don't know of anyone specifically who does that, though I'm sure they exist. Why not just pay your little brother or some neighborhood kid 10 bucks an hour to package and ship stuff? You can sell through your own website and just buy the shipping materials cheap online.
It works for me...
Peter