CB Gitty has them and you dont have to deal with eBay, as they are a legit vendor of cigar-box and similar instruments for over 10 yrs now, and also sell on Amazon but do not offer Prime nor free shipping, so no advantage there as opposed to ordering direct.
HOWEVER, FWIW you might want to consider that these bridges have the string-to-string spacing at about 10mm which is quite a bit closer than MOST nylon strung ukuleles, and closer to the string spacing at the bridge on an electric guitar like a Fender strat style.
What this means that for a player who is accustomed to a nylon strung uke, 10mm string spacing is a ROYAL P-I-T-A for finger-picking and requires a plectrum (which I've stopped using a long time ago).
Those bridges are easily available on eBay and you will find them by searching for a "tenor guitar bridge". They have exactly the same string spacing as electric guitars which is 10.5mm. Since they are designed to work with standard electric guitar pickups then this is all that can be done. If you want ukulele string spacing then you are talking about custom parts.
I've contemplated doing this before and my solution would be to custom fabricate the bridge plate similar to what you pictured and drill the holes at the spacing required. The saddle pieces are standard electric guitar saddle pieces and I would use a blade type electric guitar pickup.
EDIT: The picture is from a Risa Les Paul model of course. Those pickups pictured are proprietary to Risa.
When I started collecting parts a couple years ago my thoughts for pickups went to the p bass style pickup. With a switch and some creative wiring these can be made to switch between the two or use both as a humbucker.
BTW the pickup under the cover on the KB looks to be a fairly cheap pickup judging by the size of the magnet on the bottom. I had to totally shield mine with foil tape to stop hearing the 60hz hum of my wiring.