Definitely not OE; that stuff is way too expensive (over $110 per side).
This is a brand called 'John's Autoteile'. I purchased these off Schmiedmann's website and have them on the E39 as well. They cost about $15 per side and I threw them into the order alongside the euro clears to make shipping worthwhile.
I was hoping the clears would be some OEM brand (they don't advertise the brand) and was massively disappointed to find they're Depos. I could've gotten those here if I wanted crap, but... whatever. They'll do for now. Their products are hit or miss, but so far all of my personal experiences with Depo have been negative.
The BMW P/N for the mirror glass is 51168250438, which is the same part number on the box of the John's packaging. The fit perfectly. We'll see if they last any considerable amount of time.
Don't hold your breath; it's gonna be along time for there are any other big purchases for this car.