Where I live in the states, I ONLY see Muslim women together, never alone, and with 3 minimum. I've never seen 2 out alone. It's usually a group of 5 to be honest. I've also never seen any non-Muslim guys approach them. I bet that they'd be very taken aback by this, taken out of auto-pilot, and very accepting (as they'd view you as a dominate, non-judgmental individual). I've also never seen Muslim women at clubs or bars. (I'm talking about Muslim women that wear the hijab: devout Muslims.)
I also don't hear them talk English much. I assume these are more "Muslim immigrants" than "American-born Muslims" -- but I don't really know to be honest. Learning the language of the Muslims in your area could be helpful (Arabic most likely).
In college, I went to a Mosque for my a Religious class I was taking. They are very accepting of guests and provided us lunch. Get a friend and call ahead to ask when their "guest" days are. Women and men are separated (men in front; women in back; in fact, this is how Christianity church services were back in the ancient days -- after Jesus died, not during his life), but before or after the service, you may be able to talk with some. Before the service, it may be rude. I was there for a class, so I don't really know the custom for talking with women as that wasn't my intention. I know you have to take your shoes off, and you sit on the floor in a "guest" section separated from the men.
I'd suggest opening with a warm smile, even though it's usually suggested not to smile with teeth showing. I don't think you'd want to come in with an aggressive James Bond style as a non-Muslim approaching. It'd be good to study customs for your area. Maybe open with, "Hi *warm smile*, I don't know much about Islam, but is it okay for me to comment on how beautiful you are?" Just coming in genuine and sincere -- not judgmental or aggressive -- is probably the key, but still apply everything else you have learned here on GC for the rest of the conversation. Or maybe open with, "That hijab still doesn't hide how strikingly beautiful your features are!" Here, you're showing relatability by knowing some Muslim wording.
Experiment and let us know how it goes! I think it will make most people very nervous to approach (since you're both "different"), but because Muslim women are generally shy and nice (from my experience), then you're probably safe once you get passed the opening.
(I apologize to any Muslims reading this for how many stereotypes I'm making in this post. It's meant to just be a general view based on my personal, limited experiences.)