Generally speaking, you cannot choose a dealer. Aloha distributes software by zip code, and you have to buy from the dealer in that zip code, with few exceptions. You can purchase service from anyone... no rules governing that. But my guess it that you want the same guy who sells you the software to install it too. They are fiercely loyal to their dealers. This is something I have been battling for a while now, and it is somewhat frustrating. The local dealer in my area has a very poor service record, and there are stores that want nothing to do with them when they upgrade or open a new restaurant, but they have little choice.
There may be an exception to your situation. For example, it's possible because LA is so huge, there is more than one authorized dealer. That I don't know. There also used to be a rule that if your restaurant was part of chain that was greater than 25, you could buy the software from anywhere you wanted.
Like I said, I am not sure what your situation is, I just thought I'd make you aware of in case it's as I decribed, so you dont do a bunch of research, only to find out you have to buy it from one source anyway.
Keep us posted!