I started doing research on this too. I have a JK and use my cruise control ALL of the time on it. I'd love to have cruise control on my TJ. As many have said sourcing the parts is nearly impossible - I found most of them except the wiring harness. Since I have an '01, I am fairly certain I am not pre-wired. I took off airbag module and there are no wires running there. I see nothing under the master cylinder, either. From what I've read this is somewhat expected, I think only '03-'06 have it prewired by default. Sorry OP yours is not, that is frustrating.
I am looking at the Rostra now. Any gotchas I should be aware of? Is it possible to mount the control module inside the jeep somewhere to avoid the heat issues? On a scale from 1-10 how hard was the install? I have done some wiring, moderately mechanically and electrically inclined. Done headlight kits, trailer wiring, splicing, soldering etc and various other types of installs/repairs.