Some 26" (559mm) modern replacement rims should be compatible– but looks to need 28 spokes (versus usual 36!); looks like some re-spoking may be in order anyways.
Modern rims will fit 26" x decimal 1.5" or 1.6" modern tires.
23" rim + 1.5" + 1.5" (both sides of tire) = 26" wheels