If produced correctly, wheel rims have to be dimpled and have the holes for the spokes punched at an angle to suit the hub it is going to be laced up to (this ensures the spokes are pulling straight and not being subject to unnecessary strain). Any reputable wheel builder should be able to supply your rims, but they will need the dimensions of your hubs (spoke flange diameters and distance apart). If they are not doing the wheel building, they will also need the diameter of the spoke nipples you have (usually .300"dia on postwar Douglases).
Regards,
Eddie.