Microfasteners.com (again) you can get 100 for a couple bucks in sizes up to #4, then they start getting more expensive as there is real metal involved. However when you get really small stuff they also get more expensive. They stock metric and imperial, but some of the really small sizes may not be listed on the website. Shipping to me has never been more than 2 days, but I only live one state away.
Alternate sources are any shop that carries radio controlled model helicopters, lots of tiny metric screws in some of those birds.