TromboneChat

King SBBAR System Blue
http://www.ebay.com/itm/King-SBBAR-System-Blue-Baritone-Mouthpiece/182244905655?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D41451%26meid%3Dadf1efee680e4944a5d3aa154aa46e80%26pid%3D100033%26rk%3D2%26rkt%3D8%26sd%3D182646688774

and

JC Custom Jazz

http://www.ebay.com/itm/Trombone-Mouthpiece-JC-Custom-5L-Jazz-Small-Shank-King/172566114129?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D41451%26meid%3Dadf1efee680e4944a5d3aa154aa46e80%26pid%3D100033%26rk%3D4%26rkt%3D8%26sd%3D182646688774

Never heard of either of them.

We have had a few of the King System Blue pieces come through the shop.  These were a part of the short-lived System Blue marching line from King.  I have found them to have quite rounded rims with fairly heavy blanks.  They seem like ok pieces for the right player but nothing terribly distinguishing about them.
  I have seen the JC pieces pop up online every so often.  Besides knowing they are made in San Paulo, Brazil I don't have much direct knowledge of them.  The blanks remind me of Monette trumpet mouthpieces though...

It's a part of a series of King mouthpieces for the whole drum corps, specifically made for System Blue-affiliated corps (Blue Devils, Oregon Crusaders, Guardians). The whole line up is mostly just clones of popular sizes with the same styled rim, maybe a little other changes. They are as follows:
A lead trumpet mouthpiece (original)
A section trumpet mouthpiece (3C)
A mellophone mouthpiece (6V)
A baritone (6 1/2AL, small shank, possibly a bigger backbore)
A euphonium mouthpiece (purportedly a 5G)
A tuba mouthpiece (either a Helleberg or a Perantucci PT-88, but it doesn't matter, they apparently suck)

I used the euphonium mouthpiece for a little while last season on my marching baritone, and it was just a regular 5G, maybe a little deeper cup. However, the rim was crazy comfortable and (at least on the Yamaha baritone I was using) articulations spoke out so well it was scary.

I was considering buying a SBBA mouthpiece to see if that came up in my jazz playing, but I'm transferring schools and I'm unfortunately not joining band, and I don't have my own instrument.

The System Blue euph mouthpiece matches pretty well with, you guessed it, the System Blue bariphonium. I have a couple. Not bad pieces, but not good on trombone.

After doing a little googling, the other mouthpiece is a Brazilian made custom line, like Kieth pointed out. The website says, after a little personal translation, that the specs for the 5L are Quote* Outer Diameter: 38.10 mm * Inner Diameter: 24.50 mm * Backbore: Medium * which on their table they compare to the Rosolino piece. They have 11C, 5GS, and 6 1/2 models, but peculiarly also Schilke 51 and 52 sizes.

After doing a little googling, the other mouthpiece is a Brazilian made custom line, like Kieth pointed out. The website says, after a little personal translation, that the specs for the 5L are Quote* Outer Diameter: 38.10 mm * Inner Diameter: 24.50 mm * Backbore: Medium * which on their table they compare to the Rosolino piece. They have 11C, 5GS, and 6 1/2 models, but peculiarly also Schilke 51 and 52 sizes.