Rocket Coaxial Jumpers

I would think any Ubiquiti dealer could get them.

Flytec Computers
ISP Supplies

(to name a few)
 

I'm looking for the same thing, and while those places do have them, they all want $10+ per cable, plus shipping.  $30 for two six inch jumpers isn't too good of a deal in my opinion.
Have seen a few other cables listed on the supplier sites, but they're usually far too long to be usable.

Need to spend some more time on ebay and see if there's something suitable.

You might try heat shrink tubing after you get it tight, then a layer of electrical tape, then "linerless splicing tape" which is like "Coaxseal", then a layer of electrical tape over the top of that. One secret is to make the first layer with the adhesive in for the first turn, then fold it over and make the rest of the wraps adhesive out, to make it easier to remove if you need to remove the wrap. 

No boots, but the above comment about splicing tape may make sense. (Actually these look pretty well heat shrinked too)

https://www.ebay.com/itm/131039995018  (custom type 6" 10$ including shipping)
https://www.ebay.com/itm/151015396424  6" RP-SMA to RP-SMA $5.10 if you wait from China.
NOTE: both of those are semi rigid coax, I'm not sure what shipped with the Ubiquiti antenna off hand but I rember it was stiff, it may have very well been semi-rigid.

I wonder if the boots are needed or not. I'm in California so I'm not a fair test but I do have an antenna with off the shelf 12" cables (they use to sell them at Frys) but I don't have any boots or protection on them but they could fail in the future I suspect (don't think they were adhesive lined) I can't imagine the boots actually add that much moisture protection.