I haven't a clue but I can suggest you go to a quarry or gravel pit or a landscaping center that carries the rock you want and see if they have any brochures. It will take some time on the phone but it's better to let your fingers do the walking.
I can tell you that River Rock is a general term usually refering to rock larger than 2" in diameter. Rounded River Rock might be what you want. So, before you buy anything, find out exactly what type of rock it is you want before you go calling around. Stop by a home that has it and see if the owner/builder can tell you exactly what it is. (Hey, even ask where he got it!) This 'area' of landscaping is somewhat confusing so do be careful.