I asked about em23 and they are quite expensive. Something like $50 or maybe even more. Note that this is the cap *without* the FET, so you'll need that. I think there is an em68 or something like that too. I'm guessing (based on appearance and what others have said) that this is what is inside the AT822/825 mic. If so, this is a very nice capsule, nicer than the em23 imo. I really like the sound for acoustic recording. Not so much for amplified rock. The em68 comes with a fet as well, so it is ready to use. I forget the price for this, but it was somewhere around $50 each too. I was at one time considering getting four of these to build an ambisonic mic, but have moved over to omni capsules now.
Richard
the em-68 looks very nice, though i would think it's quite expensive as well.