You need to specify hub and rim dimensions- The diameter at which the spoke holes sit on the hub, the flange offset from the centreline of the hub, the effective rim diameter and spoke offset, if any. Probably best to ask Adam though
True story: I've been riding trials for over 10 years, along with mountainbikes and BMXes, had numerous bikes, 20", 24" and 26" and have never bought spokes. Have only ever bought complete wheels/bikes and then reused spokes several times over when replacing components. Ah well.