A varied selection of cleaning supplies would be helpful.

Tube brushes from small 1/4 inch to large 1 1/4 inch soft and stiff synthetic and metal bristles. The same for tooth brush and end brush styles. The smaller sizes aren't easy to find anywhere.

Good quality cleaning ultra sound equipment would be helpful.

Screwdriver bit sets that have a large assortment. Same for pin punch sets

A good variety of screws and hardware in small and unusual sizes. The taps and dies to go with them too.

A lot of the gun stuff would be useful to other people that work with metal stuff. The people that work with minitures often use the same types of tools gunsmiths use. Check the hobby stores like Colpar.

You need to concentrate on stuff that people want right now not in a few days off the internet. That's why I mentioned hardware and pin punches and screwdriver bits. They can stop a project dead.

You need a plan to get the word out too.