I recently discovered that my BLI I-5 was missing not one, but both of its tender truck mounting screws. I'd found one along the ROW, not knowing at the time what it was but putting it aside anyway, but I never did find the other one. I'm sure it's between a couple of ties somewhere...
They're very tiny screws, so I contacted BLI for replacements. Since I got this engine about 10 years ago, I wasn't sure they'd even bother replying, much less send me new screws. So, armed with the one screw I had, I went to our local hardware store to try my luck at finding a match.
Surprisingly, they had what I needed!
Now, they're not a perfect match - they're flathead rather than phillips, and silver rather than black - but the threads/diameter/length are spot-on and they go under the tender so won't ever be seen. And even though I only needed one, I got six. I figured I'd better stock some additional replacements - and I still only paid $1.25.
So next time you're looking for teeny tiny screws to replace rolling stock/loco losses, don't forget to check your local hardware store - you may just find what you're looking for!
(PS: as luck would have it, I just got an email from BLI letting me know that replacement screws were on the way, gratis. So a big shout out to BLI - they do customer service right (and now I'll have exactly the screws I need, including style and color!)