I'm not sure I've ever seen a Fourth of July romance, but admittedly I haven't made an exhaustive search. I think most people don't decide on their romance settings because it will give them a glorious opportunity to describe flags unfurling beneath the deep blue summer sky, however.

I have toyed with the idea of writing a historical romance at some point, but... well, so far it's still at the vague wisp of an idea stage. We'll see if anything develops.