Bought one of these on the off chance it'd work on a woodgrain 2600:
http://www.tototek.com/store/index.php?main_page=product_info&cPath=23&products_id=54
It does! Even activates on a Harmony cart like a Sega Genesis pad! Have not tried the rapid fire setting yet. Only tried an official, original Playstation joystick.
This is just one data point so it may or may not work for y'all. It's pretty sweet for me right now =)