The general answer is, "head over to Mouser or Digikey, go to the 'connectors' and 'wires and cables' sections, and search until you find something you like."
Let me offer a couple of suggestions though:
The official connector for the job would be this one: http://www.adafruit.com/products/578
. That's four-conductor rather than three, but it's what we use for other LED strips.
Another option would be an A/mini-B USB cable: http://www.adafruit.com/products/260
. We've found mini-USB connectors to be durable (that's why we use mini- instead of micro- on the Trinket) and female USB connectors -- both the full-size A and mini-B -- don't cost much. It's a four-conductor cable again, but the power lines will be rated for 1A and you probably have a couple sitting around already.
When you void a product warranty, you give up your right to sue the manufacturer if something goes wrong and accept full responsibility for whatever happens next. And then you truly own the product.