Some porn star providers give different contact numbers (email addresses too) out, usually the contact info an agency has is going to be the quickest route at getting in contact and setting up an appointment.
Clients with inside info on certain porn stars doesn't necessarily mean they have a direct line to them. For instance I have a few numbers that are legit main numbers which I can use to contact certain ladies. The only reason I have these numbers is because I know the lady well and she is comfortable with me. These porn stars usually answer within a day or so. Other numbers I've been given (personally) by porn stars are just their secondary or even "part time work" number which sometimes can take days, weeks, or (no joke) a year before they reply back.
Carmella has been associated with the following two agencies and is still listed, best to try them and see if either one has been in contact with her recently. Both of these agencies I've used before and are great to work with.
Pamela Peaks, Photogirls (they book in US as well as international)