I've purchased a bunch of wild-types and brown/splotchy Neos from members of the forum through the years. Your best bet is to post a Want To Buy thread (before you're ready to receive them) so you can spend some time finding the perfect critters.
My main 'brown' (just kinda lumping them all together) colony of shrimp has been going strong since the late 90s. Aside from wild bee shrimp (which you couldn't really keep without RO/DI water), they're probably my favorite. I'm prone to keeping wild-types, though, so you have to take what I say with a grain of salt.
I'm not a fan of hybridization and breeding for coloration isn't something I enjoy too much. With one exception - have been breeding low-grade Crystals for about a decade with a focus on getting as much red coloration as possible. Because it's not really something we see much in the hobby.
I suggested Rachel because she may have some good leads on more wild-type Neos, as I'm not certain she has any for sale.
Think you'll have the best luck if you source from a hobbyist instead of someone who focuses on selling shrimp. If you can't find exactly what you're looking for, I suggest getting some low-grade culls of various Neos. It won't take long for them to revert to wild-type and you'll have a tank full of what you want.
I had forgotten about that recommendation of Msjinkzd. Thank you for reminding me.
I am looking at the various types of shrimp. I know I dont want a color such as red, orange, blue- but patterning: spotting, striping, etc... would be interesting. The one from Aquatic Arts really caught my eye. Its very unusual.
I certainly dont have to keep fish with the shrimp. Being primarily a fish person it kinda goes against the grain, lol; but, you are right, the behaviors are what I am intrigued by. In a tank without the stress of predators, maybe I will get a more natural and productive (breeding) display.