Stinger makes any type u could want and they're reasonably cheap too. I have always got my from either bestbuy or cardomain.com. They run anywhere between 25 - 75 dollars for one.
U can connect the amp to the convertor w rca wires. Then u connect the convertor to logic7. Your gonna wanna connect it to the thickest wires on the harness of the stock amp in the trunk. They re brown for one side and red for the opposite, w respective stripes. I dont remember the exact number but they re only five thick wires on the harness. One i believe is a ground and will be useless. You will know this wire right away.
edit: this is the one im using on my car right now.
http://www.cardomain.com/item/STISLOCII