Galls.com

I personally don't buy my bags from them, but the have a wide selection. You can also try Dyna-med. The nice thing about Galls is they have black versions of some bags, w/o the SOL. Also, duffels, backpacks, fanny packs, you can order supplies, etc. If nothing else, it can give you some direction. Also, at least in the US, I believe it's some sort of crime to have the Star of Life if you're not certified EMT or emergency service provider. One of the places I worked was joined with the campus police, and one day they brought in a nice cache out of some guy's trunk after they had pulled him over. It mysteriously got confiscated onto our ambulance.

I've only worked urban rigs, so couldn't tell you about a good FAK back pack.