PicoSystem case screws

First time poster, needing some user support please. Tried emailing customer support for past 2 weeks and havent got anywhere.

Bought a Picosystem for my son for xmas. Great thing. But within 48 hours we’ve lost 3 of the 4 case screws and theyre so small that theyre now lost.

Got 1 screw left, but have no idea what type they are. Anyone got advice please? Dont know if original screws were too short either (ie. Is this the reason they’ve fallen out so quickly/easily?).

Thanks innadvance for any support, advice or suggestions - cant find anything online.