If your hub has uneven flanges you're going to need two different length spokes for that wheel build. La Casa has you covered with these nice split pack bundles. 36 spokes in a bag with 18 of each size.
36 spokes per bag. 18 spokes of each size
Brass nipples included
Rear Wheel - Single Wall
20 x 1.95-2.45" Ultra-Wide BMX Tube
Rimstrips
20 x 1-3/8" Bicycle Tube, Presta Valve