There is no longer much difference between mens and womens shorts, since they started making all of them with a seamless chamois, so if you can't find a womans short that fits, try on mens shorts as well. I'm assuming you mean stretchy lycra road shorts, not woven mountain bike shorts. Those wouldn't fit as well in a mens model.
I'm currently wearing a mens XL because the equivalent womens model from the same manufacturer isn't big enough. The mens model is available up to XXXL, the womens only goes up to a very tiny XL, which is actually pretty typical for athletic clothing manufacturers in general.