Question: I am moving a minkaire ceiling fan from a flat kithen ceiling to a sloped family room ceiling. The slope of the fm rm ceiling requires that a 1 foot extension be added to the fan to avoid having the blades touch the ceiling. The fan has a receiving unit on it that receives signals from the wall switch unit, which controls various aspects of the fan and it's lights. The extension will require me to add extensions to the wires from the ceiling down to the fan unit. All of the wires on the receiving unit and wall switch are 18 awg stranded wires. I can not find 18 awg at either HD or Lowes. The closest they have is 16 awg. Is it safe to make my 1 foot extensions out of 16 awg wire?

Answer: 
Yes the 16-gauge will work just fine. Make sure your connections are well insulated. P.
14AWG is the minimum legal size usable for AC power wiring in the US. That's why you don't find anything smaller. 

Smaller wires are legal inside an appliance or as the leads to a lamp. But if you are extending power, that is part of the power system, not the lamp, and should use the appropriate wire size for your circuit. 

Signal wires are a different matter and can be as small as 18AWG. You are always allowed to use a larger size wire, so no need to go crazy trying to find a particular size.