#I'm sorry if this will spoil the fun, but I won't tell the the exact location...
For the cow event (What I call it). You can :
1. Find the cowgirls in :
a. Transylvania/Graveyard
b. New Ark City
c. New Ark Slump (For this one you have to buy all the cowgirls merchandise? for 3 times.)
2. After that you have to talk to Bell and she will ask you to invite the Bulls
3. For the Bulls, you can find them in New Ark City/Slump