P-51 PTS, and many others www.horizonhobby.com
Many brands/models. Horizon's primary competitor www.towerhobbies.com

There are literally dozens of online hobby suppliers; these happen to be the two biggest.

www.hobbypeople.net has retail stores in CA as well as online sales.

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Before you spend any more money, do you have an experienced flyer who can help you? If not, check the AMA web site and find a club in your area. Talk to people there about the specific stuff you have and the problems you're having. You'll likely have to join AMA and join the club to get hands on flight instruction (the instruction itself should be free to club members) but it could easily be worth the price of dues in equipment and frustration savings.
The club locator is on this site
http://www.ama-dist-8.org/ActualIndex.html

There are two listed in Lancaster and one in Palmdale
Club Number Club Name
4639 94TH R/C AERO SQUADRON
114 ANTELOPE VALLEY TAILWINDS INC
1737 MUROC MODEL MASTERS*