Google reveals that a few Guitar Center stores still have them on clearance. Otherwise, that is a total oddball and it is pretty unlikely that that there is a ready made substitute. I suggest buying any 24 V AC supply, rated for 450 mA (0.45 Amps) or more. Chop the end off and solder a 1/4" TS
phone plug onto it.
What kind of a
mixer do you plan on using this thing with? There aren't too many around these days that don't have
phantom power built in.