Hi Ollie,
in this site you can find instructions with sizes, for a hat very similar to the one you want (but no pattern): http://www.northwestjournal.ca/XII3.htm
In this one, there's a lot of hat patterns, see if you can use one of them (it's a russian site, use google to translate it): http://www.crown6.org/publ/6-1-0-5083
Here is a photo tutorial for a similar cap, with instructions but no pattern (is for a child, you'll have to adjust the size): https://mushroomvillagers.wordpress.com/the-eddie-cap-tutorial/
Finally, the pattern you want, but for sale: https://www.etsy.com/listing/244615996/fiddler-fisherman-hat-pdf-sewing-pattern
Hope these are useful to you!!!