You can establish an on-line handicap by using:
http://www.ushandicap.com/
You will need to pick one club you play as your home club but that is not really important in the whole scheme of things. I use this system and it provides an official USGA index. My index is currently 10.7 and you can look it up using my ISAACID = 98653 if you'd like to see how it is derived. The only negative with it is that you will need to print the handicap card on your printer and glue it to a card if you wish to carry it on you.
To my knowledge there are two systems in the US that maintain handicaps. One is the GHIN system and the other is the ISAAC system. Both are valid for tournament play.
Hope this helps.