Hello!
Once I was building a M-48 tank, and at one point I also noticed that I don't have one road wheel. I don't know any more if I lost it (didn't find it for like 13 years now, even after renovating the room), or if it just wasn't there at all (doubt it). That's when I made my first resin casting to replace it. See if you can spot it on the photo:
The other day I was building a resin 1:72 M110 howitzer. I was just working on the drive sprocket, when something distracted me - door bell or something like that. As I wanted to go on with my work, I couldn't find that sprocket anywhere. I looked around for about a month, then just scratchbuilt another one:
Like a half a year after finishing it I was showing a fellow modeller my paints and stuff, and that drive sprocket fell out of the cap of a bottle of Mr. Mark Softer - it's shaped like a pipe and the sprocket was inside. Go figure!
Apart of that I'm usually able to locate the parts I lose - with a help form a flashlight and trying to watch the part as it flies off and listening for bounces . It's also good to try to minimize the chances - always keep the part close to the table and well over it, don't squeeze the tweezers to hard to avoid catapulting the part, watch while cutting, don't breathe to hard and stuff like that - dozens of lost details create reflexes
Anyhow, thanks for reading and have a nice day
Paweł