Sorry kiddo, you have to be 18 to get a tattoo in Iowa regardless of consent. Any place willing to tattoo you is breaking the law, and not a safe place to be tattooed at. Period. If they're willing to break the law to make a buck tattooing you, imagine what sterilization procedures they might be glazing over, or skipping all together in order to lower overhead costs.
It's just not worth it. Wouldn't it be horrible to get this tattoo for such an honorable reason, and then end up with Hepatitis or HIV? That's not what your friend would have wanted for you.
However, if your mom isn't opposed to a road trip, the neighboring states of Missouri, Nebraska, South Dakota, and Minnesota all legally allow minors to be tattooed with parental consent (in some of them, the parent must be present for the tattooing as well). But as a warning, this does not mean all shops in these states will tattoo you. Shops can and do set their own age limits, as long as it's withing the law. If you're going to visit a shop in one of these states, do a little research and call ahead to be sure that they will do it. You'll also probably have to book an appointment. Especially if it's a good/popular shop, you probably won't be able to walk in and get your tattoo.
Good luck. And if all else fails, remember, 18 is only two years away. That's not too long to wait for a good, safe tattoo.