There are several USB TV/FM tuners on the market (I have one myself) but I don’t think there are any AM tuners out there.
Wow. I didn’t even know such a product existed. I’ve been trying to find an FM transmitter that I can plug in to my computer at home and transmit audio from website such as Pandora and AOL radio to an FM frequency on a large stereo system in my living room. Most FM transmitters I’m finding are only designed to be used in conjunction with MP3 players in car stereos for some reason.