if the original wheel was laced cross 3, try the 2 speed with cross 4, I did that once and it worked with the existing spoke length
I found some info on the CABE about this very topic, single speed to yellow band 2 speed.
The yellow band diameter is 1.06 inches wider than the usual one speed hub. Using that info on a spoke calculator I figured this:
With a 26" rim, your present spokes are about 258mm at 3 cross. Guessing the flange diameter at 60mm for your one speed, and 86mm for the yellow band..
To lace up the rim to a yellow band hub at 3 cross, the spokes would be about 253mm, 5mm shorter.
To lace the yellow band at 4 cross would need spokes 266mm, a lot longer than your present spokes.
This is guessing, I would need to measure your hubs, rims, and spokes, then use this calculator to see what would fit.
https://www.prowheelbuilder.com/spokelengthcalculator
edit: I just read rickpaulos post, the spokes may be too thick, so they won't work, but you may find a wheel from an old 26" mountain bike or beach cruiser that will have similar looking spokes that will be a match in patina to your front wheel.