I have yet to come across one that works. I took one apart to try and fix it and despite being very, very, VERY careful, it broke while I was trying to get it loose (the gun platform... I forget which one's the BB and which one's the Artilleray...)
The two accessories that I have the worst luck with finding in good working order are the Dragon Walker and BB/Artilleray. Cliff Climber and Scubattack aren't far behind them.