You aren't fully being told the truth. With an M1 visa you are legally only allowed to work ONE week for every month of training. So if it took you 6 months then legally the school could only employ you for 6 weeks. Please note the word is legally as many people in the past have worked for longer periods, but a promise isn't worth the paper it is written on.
What you are looking for is a school that gives you a J1 visa. It is a 2 year visa which allows you to legally work after the period of study in the area you trained in, therfore as a flight instructor. You can also legally work for ANY company in flight instruction not just the one that trained you. The following link gives general information about J1 visas.
http://travel.state.gov/visa;exchange.html The really good part of this visa is any wife gets a J2 visa which allows them to get any job!!!!
For the J1 holder it is very important that you don't mess around. If you can get all your ratings in 6 months then it gives you 18 months to find a job and build those all important hours.
I don't know of any J1 visa fixed wing schools in San Diego but the following link will be of use to you as they are west coast based but further north.
http://www.sierraacademy.com/visas.asp
In order to become a M1 or J1 visa holder the schools have to go through hoops. And have to be checked every year. This does mean that they have to be of a certain standard. It doesn't mean they are financially sound so as mentioned in other treads don't pay all money up front and only pay with a credit card!!!
I went for it 7 years ago, built up time as a flight instructor and don't regret paying the extra to work legally in the US whilst on a J1. Only difference is I went rotary so can't help much with contacts etc.
Just as a little footnote a M1 visa school will never tell you about a J1 visa and its advantages!!!!