yet another from pa

My name is David and I am from Clarion pa, frequent Grove city and sharon as well. I ride a '93 300ex, slightly modified, still working on it. Always looking for riding places and people to ride with. I do have a question right off the bat, the castle nut for my ball joint fell off on the trail today, and I need the part number or somewhere to get another one. I have tried the hardware places around here to no avail. I am going to hit up my local atv shop tomorrow but I just figured part number in hand would make it easier.