If something is not in the main tree, it's best to open a request for
new package bug to http://bugs.gentoo.org. Granted without a user
submitted ebuilds we are not that actively adding new packages but at
least we know there's a need.
Ok, the jury is out with a verdict. If you want to run jstock on
Gentoo, you're probably best off downloading the binary they
distribute. Just unpack it whereever you want, chmod u+x the shell
script runner they have, and rock'n'roll.
I tried to type an ebuild for jstock, and out of its around 20+
dependencies most were available either in portage or java-overlay.
However, notably jhotdraw wasn't, and while typing an ebuild for it I
came to the conclusion that the missing is probably for a reason.
Jhotdraw7 would want jdo 1.0.1 jar (or something, cannot remember
exactly, it was a couple weeks ago already), and I couldn't find its
sources before I decided to go with the binary solution.
HTH if anyone else is looking at JStock. It seemed to run nicely from
the binary package.