Now more than ever, there are options of where to buy your cage. I would avoid the in person sex shops if possible. They do carry cages but be careful what you buy. Often adult stores sell overpriced novelty cages that well… are crap. Below you can find a few sites that I have bought from that have great prices and fast shipping.
#2 Lock The Cock
This site is great, they always have badass deals and sales. If you spin the pop-up spinning wheel you get an extra discount, although I think it always lands of 15% off.
#3 ALI EXPRESS
Im always slightly weary of these overseas knockoff sites but they seem to provide decent quality materials in this realm. You might have to wait a little longer on shipping.