Do you need it for the actual "high score" save or the free play?
There's a dude around here named Adam who makes a kit that you can install in any game for free play. It's way cheaper than one of the BRAZE kits (which ARE awesome BTW, not knocking them at all), his site is http://www.onecircuit.com
No high score save but it works really well in my machines.
http://arcade.souzaonline.com/ - has DK free play with attract mode ROM images in the Downloads section. Just burn (or have someone burn) 2 EPROMs and replace the ones on your board with them.
I tried the DK Jr. version in MAME and it worked just fine. No affect on gameplay. I just got some EPROMs in the mail yesterday, so I haven't had a chance to burn and install them yet.