First, you should read the stories of some of these spies, especially Nathan Hale. There's a link from our Revolutionary War Spies page to him. (The Spies page has a button on the NavBar to the left.)
On the same page, the Spies page, I have added a link to Amazon's Adult Colonial costume. Flip through the Amazon carousel that's at the top or bottom of the page. It's much more inexpensive than I would have guessed at $34.58. I'd try that.
Keep in mind, spies didn't dress in special ways. That would ruin their spying! Spies have to look like everyone else so that they're not noticed.
As a result, I added a second link on that Amazon carousel to a "Colonial Male Adult Costume." That would be more realistic because it's more common, but it's not as cool as the Patriot costume. The Patriot costume is authentic, too, but it's not what a spy that's trying to look common would wear.
I'd do the Patriot one as authentic enough, but also impressive.
