I rather like these, I have a pair in purple but they go do up to 42"
https://www.ebay.co.uk/itm/302700668...m=302700668191
Have contacted them and asked if they'd make 46.5" as a challenge.
They are a small company in the UK and might help out.
But sorry, they won't.
Slazenger do a XXXXL swim brief almost his size:
https://www.sportsdirect.com/slazeng...lcode=35216822