You'll need to do some googling to figure exactly what you want but
once you have an idea a few pointers I can offer a

1. Blum is a very reputable brand. If you buy their better lines they
will work for a very long time.
2. Try wood workers hardware http://www.wwhardware.com/. I needed a
bunch of 150 LB capacity undermounted slides a while back and found
these guys had unbeatable prices. They have a massive selection too.