I usually just lurk around here, but I guess my quest to find these finally ushered me into making an account.
I've looked everywhere to find knickers/kneepants/trouser shorts similar to those of the early 20th century (whatever you want to call them) that are attire-worthy, and NOT for costume or reenactment purposes. Everything I find is either vintage or not produced by the company anymore. They should be cut in wool flannel, twill, or gabardine, and not billowy like golf knickers, but cuffed at the leg. I performed a SF search too, which brought up classified sale listings with pieces made by Woolrich Woolen Mills, but it seems the company isn't making them anymore.
Here is a pic of a pair Brooks Brothers used to make: