There are a couple varieties- some have multiple sections ganged off of one shaft, others have a concentric shaft that allows the two pots to be adjusted independently (for example for fine/coarse adjustment on old-school oscilloscopes). Tek had some wonderful variations that would expand out a waveform when you pulled the shaft out and twisted the knob. There are some modular pots that satisfied the first need, but perhaps not the 2nd (see below photo of a dual modular pot):
I would call your example a dual pot with concentric shaft(s). You can see a smaller version with similar functionality in the photo below (taken from this web page:
If you are looking for a repair part with specific shaft length and finish it may not be easy- finding a donor unit to cannibalize may be your best bet. For production parts, the pot manufacturers will generally make what you need, subject to minimum quantities in the low thousands for some makers. There are a tremendous number of possible variations- length of each shaft, element resistances and tapers, bushing thread and length, shaft D-length or other end finish, etc. Your chances of finding one that is exact are thus rather slim.