Klingspor do them... so any klingspor dealer should be able to land you some...
We call them combination pads at work.
Some people call them interleaved discs.... Klingspor SMT850 are the ones we tend to use.
@Parm depending on what I was sanding a fresh mig weld 40grit flap disc then to higher grades and mops/cutting compound too
You also need to know how to use a grinder. If you need a hand just shout
I fear your woodturning lathe may be too slow Parm, what does it top out at, 3000rpm? The discs are designed to run on a grinder.
Most important thing will be to work through the grades, then on to conditioning pads and so on.