Roxy - can you go to a locally owned nursery (not a box store) and ask them? Or see if they have crepe myrtles for sale? So long as they get water - crepe myrtles aren't desert plants - I don't see why they wouldn't grow in San Diego.

Pruning - an arborist?? Or talk to your county extension agent. They generally have a master gardener in the program or know who to call.