Is there a store for bigger selection of screws, washers, etc... ?

Lowes has a better selection than Home Depot. For other very specific things, you can use brafasco but they would need to order as they don’t stock a lot in store.

Fastenal or Acklands Grainger.....walk in, tell them you work for a large close-by company but are buying for personal use.

Lowes weird drawers in store have a lot of stuff, but I don’t recall seeing screw extenders in there.

toyopl wrote: ↑ For example looking for tiny screw extenders this time

Without something to compare the size to, "tiny" makes me think of the extenders used in computers. Have you tried a local shop that does computer repairs?

Your picture is from fastenal try there

Before you look everywhere for this, are you sure you need a screw extender? It might be better to simply buy a longer screw.

Our local hardware store used to carry a huge variety of screws, bolts, fasteners etc in aisle full of drawers. They maintained it through several changes of franchise, while under the same ownership. Eventually the ended up as a Rona store, and got rid of it all and replaced it with the usual small selection of mostly packaged and overpriced stuff. I ran into the owner one day in the aisle and asked him why they didn't carry that nice selection any more, and he just shrugged and said "the store makes money selling $100 tools and $1000 appliances. It doesn't make money selling 5 cent fasteners.".