I don't think it matters what transducer you use as long as the connections at the unit match up and you don't have to mount it on the transom. The installation guide showed a way to epoxy it to the center of the hull on the inside. I'm pretty sure you can find one on the lowrance web page though. I just looked it up and the units can be purchased with or without so I'm sure you can get one separately. If you're close to a west marine, maybe try checking there.
http://lr.factoryoutletstore.com/cat...ansducers.html Try that link. They have the transom mount for 80 bucks. Product # 106-71