Try here for LF first https://www.backyardchickens.com/t/400344/heritage-large-fowl-thread for your Jersey Giants -I couldn't find these "breeding threads" you mentioned. Are they under the individual breeds?
Okay. father to daughter is okay, but brother to sister is not very good. Thanks.
I do have a breeder friend nearby, so I can trade roos with her each year. lol
Bantam Cochins go https://www.backyardchickens.com/t/195235/cochin-thread - it seems very active.
It looks like BYC needs help with it's breed discussion "sticky note page" - Of course, since anyone can start a new thread, same topic any time, I think it is probably a windmill chase LOL.
Browse here for other possibilites...
https://www.backyardchickens.com/f/14/breeds-genetics-showing
You don't have to trade roos every year, just once they start being infertile. You really should sit your breeder friend down, ply him or her with good coffee, set a tape recorder nearby and pump them for information! It's more efficient, really! That's why I'm so excited to have made such a connection with a gentleman south of me that has been breeding single comb heritage, SOP bred RIR's. He's going to help me with pairings, working on traits such as laying and meat production, etc.
Have fun!