To DX the AM broadcast band the best thing to do is get a loop antenna (like the Terk, Select-A-Tenna, and Eton's AM loop antenna) or something similar. They will out perform most outdoor SW antennas for DXing the AM band, and will work with any radio that has an internal AM band loopstick antenna.
Or you can make your own loop. All it takes is wire, a frame (a box crate will do), and a tuning capacitor.
You set the loop next to the radio and tune it, and it peaks the signal (and boosts it on most radios).
Like N5IMS said, there are plans on the internet to make them. But you could buy an factory made loop for the AM band for $30 or less either on the internet, or at some electronics stores.