This is the battery I found for the scope. It's a Panasonic lithium 3V battery that cost me $10. It's a tight fit, and I may have scraped down the little retaining part of the cap getting it to close, but it fit almost perfectly and is the right voltage and makes the reticule light up, so yay!
Here's the empty chamber, locked back. Again, sorry for the poor quality. You can sort of make out a triangular stamp behind the takedown lever.
Here she is, put back together with the scope on. Ain't she a beauty?
And the money shot. I call her Vera =)