pinterface - 9:32 pm on May 11, 2011 (gmt 0)
We used to have a daily pickup, though the time wasn't of our choosing: it was whenever our carrier happened to deliver mail, he would also pick up anything we had (the timing of that was pretty reliable, though). Never actually had to do anything special to get it: shortly after we moved into the building he stopped by, introduced himself, and inquired about whether we'd be shipping stuff. We said, "Why, yes, we do!" and every day after that he'd stop in, say howdy, and ask if we had anything for him.
Occasionally, he'd bring a giant stack of postal buckets for us, so we had something to put stuff in.
Buuuut...I guess you're looking for something a little different from that. I think your best bet is probably to ask the two local businesses you know are getting the service you want how they got it. While people here can give general advice, a local business can say "Oh, uh, talk to Don at the 82nd Street branch, he can set you up" or whatever. ;)