FYI, you can find metric Allen screws at local hardware stores:
https://www.lowes.com/pl/Machine-scr...ent=4294710182
The type of screws that are used in stems, seat post clamps, and other odds and ends on the bike.
So, if your screws are stripped or simply looking shabby after lots of use, you may be able to find what you need at the local hardware store. Take one of the ones you intend to replace into the store with you to make sure you get the right size and thread pitch. Look for what you need in the Metric area (most bike screws, nuts, and bolts are Metric).