C'mon Paul, someone made one. I've seen one in a Specturm Pursuit bike with a 24" front 700c set up. This was '95 I think, perhaps '96. T-town when you had to do a 1:06 to get a spot in the Olympics and no one had done it yet.
it wasnt a rev-x, maybe corima? It could have been a 650 front. We had one of the old wheaties /Schwinn TT bikes in our shop and everyone swore it was a 24" front wheel. It was a 650
I know it's not what you asked about, but there are some old Hed CX's in 24" floating around as well as some 24" front disks. I got a CX off ebay a couple years ago for pretty cheap.
Failing that, you can build up a 24" Velocity Aerohead and skip every other spoke. I've got one and while it's not as aero as the CX, it is stupid light.