From X Factory:
A major expansion of the great X Factory hardware line is here now: 4mm hardware and set screws found on most 1/8 scale cars. For many years X Factory has sold great little packs of hardware for R/C mechanics’ use in 4-40 and 3mm sizes. These fasteners generally fit 1/10 scale cars; now X Factory stocks the 4mm sizes found on most larger vehicles.
In both flat head and button head, all the popular lengths are here, along with nuts, locking nuts, and washers. X Factory also now stocks four lengths of 3mm set screws and a 4mm set screw too. All packages sell for just $1.59, so there’s no reason why you don’t have what you need when a screw is stripped or falls in the grass.
They are on the XFactoryStore.com site now and soon in fine hobby stores.