I'm British and I got mine from a download from our government's website. maybe he should try his government website as a starting point. Other than that there might be some resources available from Google searches on American websites or forums.
Try using a different browser. I think I used Internet explorer initially which gave the issue you described. When I switched to Edge I managed to get the correct options.
I send 2 parcels to my daughter last month. 1 was a higher priority one so I paid extra for a royal mail global priority (or whatever it was called) and one was sent by normal postage.
The normal one arrived in a similar 6 days to yours, the more expensive supposedly quicker one took 3 weeks.
Work that one out. Lesson learned I think.
To be fair it was held up in England for 2 weeks I think the covid backlog was the excuse.