A lot of national parks and monuments give dollar coins out in change when paying for admission or whatnot, trying to encourage their use. No one seems to want to use them, unfortunately. It's practically impossible to find $2 bills, dollar coins, or especially half dollars in regular change though. You're far more likely to find a silver dime or Canadian change in my area, at least.
I've heard in the past that the government would really like to phase out dollar bills in favor of the much longer lasting dollar coins but no one seems to want to.