Dig around at TSS Radio. They have a few different versions of the tuners for different radios, including superseded and newer models so you should find something. You may not get the Clarion branded unit, but I think they all come from the same place with different packaging anyway.
I'm sure you know this, but you'll need a second sub for the boat if you don't want to just carry over the sportser. I just lost my (3 year old) Sirius tuner in my boat this season and no luck on a replacement yet...older Alpine unit. Something spilled around a drink holder, worked it's way through the dash and fried the tuner! http://www.tss-radio.com/