If you can't get proper length spokes at local outlets, people pointed me toward Dan's Comp as a source for decent priced short spokes.

I laced a Sturmey Archer 70mm front drum and 2SC rear hub to Velocity AeroHeat rims. Used 3x pattern because that's the length of spokes I had; would have gone 2x if I'd known about Dan's Comp before ordering parts.