I don't think "cheap" for a rare or custom pair of wheels is going to be possible. I can't imagine there being many 24" disc brake wheels out there. Why not build them yourself or get them built?
24" rims should be easy to find and inexpensive disc brake hubs sure are. Add $32 for spokes and you're in business.
24" rims should be easy to find and inexpensive disc brake hubs sure are. Add $32 for spokes and you're in business.