HYCCT was advertised on the main page, which is where I saw it advertised. I also "like" the SCS Facebook group and they often put little advertisements there. I don't read the weekly inkling. LOL.
There is a whole "SplitCoast Challenge" section of the forum, so read about alot of it there. I guess I just poke around the site and see what's up. The other place that challenges are posted are in the Member Company threads. I found Verve awhile ago and play along. I know MFT is there, but I haven't played yet (it's on my list). I just went through the treads a few days ago to see what other companies offer challenges.
Most of the challenge threads have a description of the challenges stickied in the forum.
I am currently a Fan Club member (paid member), but I JUST joined in August. The reason I joined was to do their Dare to Get Dirty Challenges. I think they're pretty much the only challenges that are "restricted". I also joined for instant uploading of pictures (I don't have to wait for my pictures to be approved by a moderator).