FR's Proshop has really expanded its product lines towards milsim players in addition to their old speedball gear and garb. Belleville Boots, Truspec uniforms, UTG vests, etc.
KW Surplus has less than 1 aisle dedicated to clothing and boots and rarely has any gear. Now if you are looking for a cheap gas generator that is the place to hit or some very old electronics.
Army Issue, carries everything you need to get started (from hat, goggles, shirts, pants, boots, socks, vests, drop leg rigs, drop leg holsters, AMMO (Variety of weight BB Bastard line, whites, blacks, silca, etc. Batteries, loaders, etc.)). Basically for someone starting out, AI is your one stop shop to get going for a good price!
Be safe not just with yourself, but those you play with. If you are reckless with other peoples safety then you will leave.