I have a set of Shimano Rapid Fire shifters and they were not shifting into all gears. After a little internet research I found they just needed a good spraying of WD-40 to start engaging the small spring. That fix worked like a charm however during re-assembly the nut holding it all together popped off! It's soft alumninum and there is such little room for the nut to thread onto I ended up stripping it. These things are reverse threaded

Where can I get one? Is this something my LBS would have a draw full of or do I need to contact Shimano? I was going to try Home Depot but the reverse threading has me thinking I'll have zero luck in a hardware store with something so specific. I'm so mad at myself!