There are French Dress Shirts available online but not a white 1 - patterned, striped, & a few block colours - such as Black but no White - odd I'm sure it used to be available.
I've used the Caughtrey in white with a waistcoat [vest] & that isn't too bad.
Good call on the Grizzly Outlaw Outfit
Seems odd they haven't included what you would imagine would be 1 of the most sought after colour of shirts for many costumes - very weird.