www.visitingcatalina.com is a resource for a good Catalina Travel book. A lot on diving and operations, including mainland dive boats and contact information.
You are more likely to get good diving operations from the Long Beach or 22nd. Street landings, but Huntington Beach is not really a good port for dive boats. I recommend Encore and Great Escape as they are nice big boats. However, the boat that frequents Catalina the most is Sun Diver at www.sundiver.net. Smaller boat but worthy of a trip or two.
On-island, you have really two choices in Avalon and one in Two Harbors.
Avalon: Catalina Divers Supply and Catalina Scuba Luv have nice dive boats and operations.
In Two Harbors you have one dive shop that has two main boats, plus there is EXCELLENT diving at Ship Rock, Bird Rock and Blue Caverns within 2 minutes of the dock. You can stay in either Two Harbors or Avalon as both have hotel/s and restaurants.
If you need more help, contact me at joe@californiaunderwater.com.
Joe