Unlimited RPG ammo in Saints Row 2?

I recently started a new save slot on SR2. on my old game i had unlimited RPG ammo and I don't remember how i got it. i remember having it before i faced the final battles with the samedi and brotherhood both so i got it somewhere in between beating the ronin and fighting the samedi. does anyone have any ideas how i can get it again? i am 100% positive that i did have unlimited RPG ammo and i never used any cheats. i had completely beaten the ronin, fight club, and demo derby. my rep or whatever was maxed out and just had the infinite symbol next to it b/c i'd gotten so much. any ideas? thnx