Given that there are two of the screws and you only need one, remove the one you do have and take a picture of it on a piece of graph paper.
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There is a picture of a F6 here:
https://www.mig-welding.co.uk/forum/threads/show-us-your-bench-vice-s.52872/page-303#post-1997899
The screw to which the OP is referring is the slot head one just under the anvil behind the fixed jaw, above the 'S' of FORTIS.
My guess is that 'bevel cupped head' would translate to 'cup point' in fastener terminology.
If it is 1/2" BSW, the closest off-the-shelf I can find is at the bottom of this page:
https://www.ba-bolts.co.uk/bswallen.html
It is only 3/4" long. Buy two so both sides match or put a 1/4" long brass spacer under it.