There's a World of Crossbreeds club I believe? But it won't let you halter show your horses if that is what you are interested in. 

World of Crossbreed tends to cover any set crossbreed that isn't established and the like. It's underneath Clubs instead iirc.

So the club that sets up shows is the Crossbreed Association. How do I register for the shows?

You cannot halter show generic crossbreeds. You can only halter show crossbreeds that are part of an in progress or completed crossbreed campaign and those clubs will all have their own names.  Generic crossbreed horses can still be shown in disciplines once they age.  I'm not sure where you're seeing a crossbreed association that does shows could you elaborate?  I have several generic crosses and they've never been able to halter show which would be the club run shows, but they are all registered with World of Crossbreed still so I can keep track of their star value.

You can find shows set up in the halter arena

Yes I understand about the halter arena, I'm asking where you saw shows for generic crossbreeds.  The clubs available for showing under in the halter arena are all either purebreed registies or crossbreed campaign registries.  Where are you seeing shows for this Crossbreed Association you mentioned?

https://horsefable.com/halter-show/96aef19d-bdf1-450d-9489-0e4051187b5b

Here's a link to one of them

I think those might be shows from some of the reset breed clubs.  I grabbed a crossbreed stallion from the rescue and registered him with a couple of different clubs but cannot enter any of those shows and  I find it extremely unusual there's so many shows with Crossbreed Association on them in the arena, much more than any other club but I have noticed in the past the crossbreed campaigns that got deleted for not meeting the activity standards still technically exist as clubs but now all have Reset Club as their names, I wonder if their shows got turned into Crossbreed Association the same way.  Staff would have to look into it and confirm that's what is going on, but if what I suspect is right you still cannot enter generics into these shows because 1) the clubs no longer function and 2) the crossbreed would still havhave to meet the breed percentage requirements of the specific clubs.