In JA2, you have to unlock Bobby Ray's. You can find the website via the AIM website's links page before landing in Arulco, but even then it is "under construction" until you liberate an airport. Then, as others have mentioned, there is a progression system to their inventory that mirrors your game progression.
Also, even with access to Bobby Ray's, I would still visit Tony and other vendors as often as possible to find different items (specialty weapons, electronics and regen sticks to name a few). Bobby Ray's definitely helps level your equipment up if you have the cash, but it doesn't have endless inventory either.
I remember using it more for ammo (7.62 NATO/WP, 40mm grenades, mortar shells, grenades and the occasional LAW), accessories (NGV, med supplies, tools) and armor (and plates) than for weapons.