opening car door

Check out a wargaming store. They usually sell tiny disc shaped magnets in various sizes. Your local hobby shop may have them if they sell wargaming supplies.

Do a google search- great for finding sources of stuff like that.  A company that used to be called Edmund or Edmond Scientific now has a new name- forget what it is, but they have a lot of magnets.  Also a company called, I believe, American Science and Surplus has them.