Extension cords

Another DIY option would be to start with a Hubbell 4 Plex outlet mounted in the matching box with your choice of plug and cable at whatever length you need. Like this:
Hubbell 4 Plex

Signal Cable will make you an extension cord or a long standard power cord. I purchased a 3m standard cable which powered a ps audio passive filter (what is the name of the damn thing?) for something like 70 bucks; still have it and no longer use it.

I am sure an extension cable can be made if that is what you wish. The longer the run makes me want a higher quality cable/insulation; makes me feel better.

If you don't mind a little DIY, HD has 10 AWG twisted, stranded (for EMI, RFI rejection) Carol cord in bulk. They also carry some excellent male/female AC plugs that are very easy to wire (they're yellow, can't remember the brand.)