www.musikding.de
Yep, that was my rationale for buying a dozen dual reverse audio taper pots from them a while back. I needed long bushes for mounting my "filter" preamp in a back routed bass and I reckon someone else will sooner or later too. Turnaround was about a month, it wasn't cheap but it also wasn't really prohibitively expensive for me either.
I think mine (dual wafers on one shaft) ran me about $125-$130 including pretty fast Royal Post shipping. A few months later I did an order for a different spec for a customer for similar money too, but he bought more and the shipping per unit came down a little. In both cases I specified the high rotation torque option, which gives a very nice feel.
If a standard size isn't available I suppose I can try to make use of that. At the very least it should be fine for prototyping. Thanks!