Hey Matthew, welcome aboard matey!!
What size britches do you wear? I think I still have an old pair of breeches downstairs.....cant remember the size, but I got them from from my Dad from the 1776 Bicentenial, alas we are both a bit broader these days! You might be able to squeak by in them until you aquire what you need/want, or if your handy with a needle, convert them over to French Flys......
OR
tell me your size, I have a pair of French fly breeches that I wear ( im roughly a 36) I'll use em as a pattern and I can stitch up a pair...you add the buttons...