It really isn't that hard to make one. You need to make a hob by
making a copy of your lead screw (left hand thread), mill a couple of
teeth and relieve it. Make a mount for your toolpost for the blank to
rotate, put the hob in the spindle between centers, and advance the
blank into it. You don't even have to harden the hob it you make a
brass gear.

It helps to gash it first to be sure you get the right number of teeth,
otherwise you might get one mor or less than you need. A spin indexer
is close enough for this step.

To make the hob without a threading dial, just don't disengage the half
nuts. It gets a little tedious and you may have to rotate the spindle
by hand at times, but it can be done.