Dish Network had some circular polarized signals on Anik F3 at 119w in the 11,700 to 12,200 Mhz range. (I believe they are gone), so there were circular LNBFs available. I have one stored away somewhere. But, like the Inverto LNBF you linked to, it uses a dielectric resonate oscillators, which drift a lot. The Inverto spec is +/- 3 MHz of drift. That is a lot when you are looking for narrow telemetry beacons.
I think it is worth a try making a dielectric polarizer for something like the Bullseye LNBF, which is very stable. The most critical thing is finding the right material. On C Band I've made them out plastic cutting board material and strips of foil on a thin sheet of plastic, but nothing worked as well as the ones Titanium provides with his C Band feeds. But those are much too thick for Ku.