<font color=navy>Do you already have a package with hoppers and a stay at the hotels? If you do, or even just staying at one of the Disneyland Resort Hotels, you can go to the Walt Disney Travel Company Office, located in Downtown Disney, across from the Disneyland Hotel, and get tickets and transfers from there.
You can also go to the Airport Bus depot, located next to the Howard Johnson Hotel, and get transportation there, then buy your ticket once you get to Universal Studios.
I took this picture of the depot & of the transportation sign at the Airport Bus depot when I was there a couple of weeks ago.