There are plenty of older hsfs out there that will fit AM2/AM2+/AM3 with the proper mounting hardware. For example, the old Ultra 120 was released back in the s478/s939 days if I recall correctly, but it can still be made to work on AM2+.
I have a Big Typhoon VX downstairs on my AM2 system, which is nothing but a Big Typhoon with a faster fan and updated mounting hardware (and the BT most definitely had s478 mounting hardware).
You might want to ask about a specific HSF, and you might want to ask in the Cases and Cooling forum. That being said, with coolers as cheap as the Mugen 2, Hyper 212+, and Contac 29 floating around out there, there's a good chance that you'd be better off getting a brand new HSF than trying to find mounting hardware to make an older (and likely inferior) HSF work on an AM2+ rig.