The "trick" with cartomizer systems is to work out the thread size/fitting and buy blank or prefilled from another vendor.
What some people find is that, actually, there is not compatible gear out there, in which case you need a new system.
I used a system with a thread that was unique. It was a way to keep users buying cartos for $6.70.
It was then I swapped to KR808-D1. That was not the best move either, so I then went to 510.
These days, I sometimes use the 808, but prices are 40% less these days than 2012.