A number of signal captures are available at http://www.kd7lmo.net/ground_gnuradio_ota.html . These are useful for developing software to demodulate signals when a USRP is unavailable. The following files from this page contain AM signals:
ATIS Broadcast (118.250 MHz)
Shortwave/ WWV Broadcast (10 MHz)
AM Broadcast Band (around 600 KHz)
The Python script for a simple AM receiver, implemented with GNU Radio is also found on KD7LMO's web page. A copy of this file with minor modifications and comments is found here. The program is run using the following:
./am_rcv.py filename offset
Where filename is the file containing the signal to be demodulated and offset is the frequency offset from center (in KHz) of the station to be demodulated. Details on each of the three examples are found in the links below.