By far the most common (and cost effective) options are:
1. Buying a new "take-off" factory top on Craigslist, the forum classifieds, etc.. People often buy Wranglers off the lot that come with dual tops...and they have no intention of ever using the soft top.
2. Buying a new Trektop NX online/from a vendor.
I did #2 first, got a great, great, great deal from Bestop outlet.com (or something like that), and never took it out of the box. Was on another forum talking about soft tops and how I really wanted a top that I could take with me when down. I got a PM from someone local who just got a brand new Rubi and wanted to straight up swap his never been used premium top (he ordered dual tops) for my still in the box Trektop NX.
Ummmm.....done! (I even threw in a $100 bucks so I didn't feel like I was ripping him off.)
It was pretty funny because I tried to explain to him all of the reasons why I didn't want the Trektop NX, and he was like...that is fine....those are the exact reasons why I DO want it.