Fitting a TV to it's stand is usually the first thing you have to do but, oddly, there's no mention of either the stand or the screws in either of the manuals. They're not even listed in the supplied accessories section.
The VESA bolts needed for wall-mounting are M8, but I guess that's not what you're after.
People of a certain age, (myself included) usually have a collection of screws of various types/sizes gathered over a lifetime sitting in a box or tin.
You surely have a relative/friend/neighbour with such a collection who could let you try some of these screws and when you find one that fits, take a visit to any of the D-I-Y stores and show it to an assistant and ask for some of the same size.