These may not be the best, but most of them are local to me.
An army/navy surplus store, so it's a fun shop aside from having a small flashlight section. They have a selection of Surefires and other no names.
Supply Sergeant
503 N Victory Blvd, Burbank, CA 91502
(818) 845-9433
It's been a few years, but when I last visited this really nice knife store they had one wall which was nothing but Surefire flashlights.
Recon-1
19423 Ventura Blvd, Tarzana, CA 91356
(818) 342-2666
I have seen a few Streamlights, Magchargers, and Surefires on occasion at this police uniform store. Not a lot of flashlights to look at but if you're looking for duty grade stuff, you can get it here--if they have it in. Just a few lights under glass near the cash register.
Quartermaster Uniforms
2543 W 6th St, Los Angeles, CA 90057
(213) 351-9632
This is a huge electronics and appliance store and they have a flashlight aisle. They have Mag, Inova, Gerber, low end Streamlights, and low end Pelican.
Fry's Electronics
2311 N Hollywood Way, Burbank, CA 91505
(818) 526-8100
This sporting goods store has a flashlight aisle as well Gerber, Petzle, Coleman, Princeton Tec: nothing weapons grade.
It's part of the shopping mall at Burbank Town Center.
Sport Chalet
201 E Magnolia Blvd # 145, Burbank, CA 91502
(818) 558-3500
If I can remember some others, I'll post again. If there really is a best B&M flashlight store, I'd like to know also.
Welcome to CPF, Kiwi_sg!