Get a decent garter belt in NYC?

I had ordered one from Frederick's along with the corset, and it's ok. I love thigh highs but they never stay up on me, so I figured I'd try out a garter belt.

Like I said, the one I got is ok. Since I ordered it I obviously couldn't try it on, so it's a bit too small. Not so much that it's uncomfortable, but I could use a size up. It was like $10 anyway so it's not the end of the world that it's not perfect.

But I want a good one, one that fits perfectly and is better quality. I'm at a loss as to wear to get one though. As you all know I'm in South Brooklyn, so I have Manhattan at my disposal.

Any suggestions?

Also, question - is the damn thing supposed to go over or under your panties? Cuz of course every picture of one on a person is worn over the undies, but I feel like it would be REALLY hard to pee if you wore it like that. I don't want to be un-clipping the straps all day/night whenever I go to the bathroom.