I have found that an aftermarket cruise is available that is made by Rostra. There webpage is www.rostra.com. The model number for the cruise unit for the Spectra5 is 250-1223. The model number for the control handle to mount on the steering wheel is 250-3742. These can be gotten new on ebay for less than $200.
I downloaded the installation instructions from the Rostra web page and checked them out. It doesn't look too hard. I haven't gotten it yet because I can't find out where you tap the VSS (Vehicle Speed Sensor) wire. Once I figure that out I'll give it a try. I'll take some pictures and post a project on it if I do.
None of the dealers or accessory stores in my area would do a cruise control. They all complained about liability issues. That didn't help me any when my salesman had assured me I could get the cruise as an aftermarket and not to worry about getting the one they had with the sunroof that had cruise. Oh well.....
I replied to your original post that a moderator musta moved.
Anyhow, I have the Rostra that was installed by the dealer's contractor. Works good on the Highway. Not as accurate as the other CC I have driven but gets the job done. Mine is located below the turn signal, which at first I thought might get ripped off by my knee, but so far so good.