100R seems very low for a volume pot, might be why you are having trouble finding it in a double-gang.
I'm not really an audiophile and don't know what you're trying to do - but I'd normally use say 50K or even 100K in my cab volume controls.
You should also consider that pots typically come with either linear taper or audio (log) taper. There are also anti-log taper types. This is because human hearing response to changes in volume is not linear.
Also, because most modern log/antilog taper pots are actually pretty crap (log curve is simply approximated by using two linear tapers), It is possible, perhaps preferable, to "fake" your own log/antilog pots from linear taper pots. This way you can even experiment with what works best for your situation.
Here's how I did it for my magenta Aussie lowboy