Again it's almost certainly supposed to be 100/126, and regardless that'll fit effortlessly anyways. You might be able to space a 120mm single speed wheel to 126 with spacers assuming the axle is long enough, or order a longer axle with the same size and pitch. This is probably what I would do. Or on the cheap you could find an older 126mm freewheel wheel, which will have the slight disadvantage of being somewhat dished (as opposed to respacing a ss/fg hub).
There's also
https://velo-orange.com/products/gra...fixed-hub-rear .