Check out the eigenbarrel.
If you want more control over the bores, look at finding a full Powerlyte Scepter kit or a Thin Air Sports GnB kit.
(close the space, idk why the site would censor it)
check out the GnB kit
Those three are the greatest known to man. Period.
Incredible bore lengths, immaculate quality and condition, and with some serious-*** porting. None of the straight hole type either. The angled porting keeps the friction, turbulence and sound way down.