I remember from reading on a website that Radio Shack parts are known by another name. For example the 276-038 is a 1458 and a 900-6298 is a 353. I would like to know what the 276-640 is so that I can find a datasheet on it, since there is no datasheet for th 276-640.
I'm not sure it has a fixed part number. The catalog page http://www.radioshack.com/product/index.jsp?productId=2049727 gives the description "38kHz Infrared (IR) Receiver Module" but I'm not sure how precisely RS defines the part beyond that. Radio Shack probably selected some particular manufacturer's receiver unit, but I don't know that they'll always use that same one. Unless you need to precisely match a particular component, I'd suggest going to digikey.com, search for "remote receiver", select "38KHz", and go from there.
On mine stamped on the top is 4838 so I would assume it is equivalent to a TSOP4838. Spec sheet can be found here: http://www.farnell.com/datasheets/30500.pdf