Welcome to the RTA Forum!

I'm sorry to tell you that with the exception of high end exotic sports cars, or other specialty rentals of that nature, you're just not going to find what you are looking for.

The Rental Car market in the US deals entirely with automatic cars. In fact, even to purchase a manual car is getting quite difficult in the US. The only cars with it even sold are generally the base models of lower end cars and trucks.

The best you're going to find is that many cars with an automatic transmission now have a "feature" where you can control the gear you're in. Its not nearly as nice as actually having a manual transmission, but it does give you some control.