Helpubookher is another agency with some porn talent in Vegas
The only one I know of is TLC.
There are three choices that I know of, in order of my preference: TLC, Pam Peaks, and 100ProofofLasVegas.com. TLC is the best choice and highly recommended. Pam Peaks has a lot of talent available in Vegas but she requires a deposit in advance. 100Proof is a newer agency that I've never worked with but I haven't heard anything bad about them. Other agencies probably also have porn stars in Vegas but I don't know any off the top of my head that regularly advertises Vegas girls.
You can also try the porn star ad board, the vegas board, and Eros. There are other sites that you can check but since they have reviews, I can't post them here because of TER's rules
Agree with MrFrench, you're first stop should be TLC. Adonia has a few ladies in Vegas and is great to work with. I can highly recommended Heather Vahn, who is based in Vegas.
Zach at 100Proof is also very professional and laid back. Easy to work with. The only one I can speak to personally from 100Proof has (unfortunately for us gentlemen) retired. So I can't speak to the rest of the ladies.
MPP also has a few. I haven't seen her in a while, but Kylie Wylde is based there and is quite a bit of fun..
Helpubookher is another agency with some porn talent in Vegas