Looks like a cheapo Promax or Tektro type brake. I'm not being a snob, but I'm not up to trusting my life to some cheap brakes. Avid mechanicals are one of the few rated for tandem use, so you know they're built strong. If you can take them off, you can compare the pad to photos online of different brake pads, which may help you identify the manufacturer. According to the spec sheet, your bike came with Tektro rim brakes. Try ebay for some Avids, or even Hayes mechanicals to get you going (sorry, stopping) for less than $100. If that's too big of a hit on your wallet right now, just get some rim brakes. They'll probably work better than questionable mechanical discs.