Lonsomcrow,
The only alternative to the 240/50ZR16 from Metzler at the present time is a car tire. Avon is close to releasing one that will fit, but the cost is supposed to be higher than the Metz and tread life is still a big question. I have a car tire installed on my Rocket and even if the price for the Metz was the same as my current tire I would not be going back to it. I'm currently running a Toyo Proxes in 245/50VR16, cost was $104.00, I installed it myself and I'm crippled. Do a search for "Darkside" topics and read about your only alternative for the Metzler rear tire.
Joe