http://www.bouncycastle.org/latest_releases.html The thing we need to decide here is what to with different versions because they seem to release a version for every major jdk release.
It seems the gcj overlay has something for this: http://overlays.gentoo.org/proj/java/browser/gcj-overlay/dev-java/bcprov/bcprov-1.35.ebuild
wltjr added 1.36 while ago. I just revbumped it to get rid of junit again. Closing.