Any bike shop should be able to help you out. It is not a proprietary item.
You'll need to determine your needs by the actual format of the bottom bracket:
1) Remove a dust cover from the crank arm (if it has one) and look in. The crank arm is held onto the bb by a bolt or nut and by one of several methods. My guess is that it is a square shank. There are some that have various spline configurations... if you have one of those you'll need to take the bike to a shop for identification.
2) Remove both crank arms from the bb. Make sure to use the appropriate tool- not a gear puller or ball joint fork. Remove the bb from the frame.
3) There should be thread and length info on the bb housing. Copy it down and go to your friendly neighborhood bike shop with the info or just take the whole gizmo to insure it matches up.
Expect to pay somewhere between $20-$50 plus the special tools if you don't have them already.