craigslist
I would have to say www.firstact.com It has some expensive guitars on there, but then again, a lot of them are really cheap.
Yes, they are found. Often suitable for one.
Ibanez is a company that is known for making cheapish but reliable shortscale electric guitars. As of July 2013, prices for their guitars range between $170 and $250 depending on the model.
Electric guitars can be bought in a lot of places online and in specialist music stores local to you. You could buy them second hand in local newspapers and various websites dedicated to the selling of electric guitars.
You can purchase cheap acoustic guitars from a wide list of stores. Stores including, Guitar Center, Musician's Friend, Walmart, Best Buy and Target.
At a rich guys garage sale. Craig's & pawn shops as well.
Gretsch electric guitars can be purchased from Sweet Water's official website. One can also purchase Gretsch electric guitar from the Sam Ash store where they carry a wide selection.
Electric acoustic guitars can be bought from many stores and online retailers. One can purchase them from eBay, Amazon, Best Buy, Guitar Center and Musician's Friend.
you can pretty much buy them anywhere but if you want it cheap that's another matter
Guitars, mostly. Probably electric ones.
you'll never see a floyd rose or whammy bar system for that matter on an acoustic , or say electric guitar pickups that are designed specifically for guitars. stoptail pieces for tuneomatics on say les paul guitars locking nuts for floyd roses knobs right on the face of the guitar like an electric on cheap acoustic guitars I've seen them made without trussrods which shocked me