Mirrored glass door

This looks like a latch for a storm window. I've never heard of one being installed on a mirror door before. Is this for a closet? If so, that's very, very odd.

Either way, these latches aren't really that common anymore since storm windows have fallen out of use. We do carry a somewhat wide selection, but it's getting smaller every year. I recommend browsing through it here. Note that because yours is installed on a mirror door, your entire setup may have been a custom construction. If you can get in touch with whoever installed it originally, I would do so. That's probably going to be your best bet.