A few options that I can think of:
1. A standalone tv tuner. I think Samsung has a version that was pretty popular. But since almost all HDTV today have the tuner built in so this kind of product is rare, and in my opinion, too expensive.
2. A settop box from cable company or satellite service provide, aka DirectTV. you can probably get a used on from eBay but you have to make sure it's what you are looking for.
3. A DVR recorder. this one has a TV tuner built-in. So if you can find some use for the DVR this will be a perfect fit.
http://www.amazon.com/gp/product/B00...SIN=B001TOD3KK