You can't find one. I should rephrase that. You can't find one that you can put up a fence with.
The largest electric nail gun I've ever seen will shoot a 1 1/4" brad nail. That's not gonna hold up a fence, unless you use a score of brad nails per panel, and even then, I wouldn't expect it to resist even a light wind...
A paslode (or other brand) gas powered unit is an option, but retails for more than a compressor and a couple of cheap nail guns. plus there's the cycle time, and you are locked into proprietary fuel cartridges/batteries
In the end, the reason pneumatic tools are the choice of pros and homeowners alike is because they work, they can be quite inexpensive, and they are durable.
If you don't want to go for the compressor I understand, but your best choice is probably going to be a drill/screw gun and screws. It'll be a heckof alot cheaper, and do a better job than most nails (even air driven ones

)