Or if your frame is made out of steel you could simply install the 120mm spaced wheel into the 126mm spaced drop outs and tighten evenly on both sides. You now have 120mm dropouts. They may even cold set to around 123mm.

Some frame manufacturers use 132.5 spacing so that cuctomers have the choice between 130 & 135mm spacing. Steel flexes. In short there really is no problem using a 120mm spaced hub in 126mm spaced dropouts. I've even used 126mm hubs in 120mm dropouts no problem.