You should be able to buy a 2-wire (or 4-wire depending on how you installed it) connector at any auto/hardware/electronics store, just make sure they will work with the gauge of speaker wire you used. Normally the plugs only fit together one way, so you shouldn't have to worry about crossing the wires when disconnecting/reconnecting. It doesn't really matter what kind of plug you choose, but I would try to get one in a dark color that is relatively flat so it is less conspicuous.
The OEM plug is black and clips to the roll bar (
picture). With an aftermarket plug a zip tie will serve the same function (probably better, since my plug never stays in place)
Make sure to mark the wires if they are not different colors, before you cut them to insert the connector.