I ordered one of the Interordnance Mk1 Bren barrels the other day. I'll report when it arrives.
I put little faith in "handpicks" from the big vendors, so I ordered the $50 one.
I can remember getting two beautiful full Bren parts sets from IO about 8 years ago, but I'm sure they're near the bottom of the barrel (Ha ha) now.
Dan is right about Omega having nice barrels. I have two of those, both NOS. They're Mk2, though.