I have a 2004 Buick Park avenue with air suspension, and living out in the country, I am tired of the bouncing and rolling this suspension gives. It'* very nice on smooth roads, but horrible out here where the pavement is.. older. So, with that in mind, is there a good replacement for the air suspension?

In this situation, you can't have your cake and eat it too....
P/A'* and LeSabres, are made to roll, to give that comfy kind of ride as opposed to a sport suspension....
You can change the stabilizer bar and struts for a stiffer ride, but most people who have done the transition, don't like later....

How old is the current set of struts? Air ride or not, if they are worn out you'll get bouncing and rolling. Combined with what Tech II said above I could see it getting crazy on the older roads.

Or if you just Want rid of the air ride You Could Buy A pre loaded Strut kit such as this one And replace them all with standard Struts This One Is Just One Of many listed On Amazon for your car

For your rear air ride only suspension in the PA, Monroe makes a coil over shock # 90007 that coverts the air to a load leveling.
This gives a nice ride and will work perfectly for your 2004 PA. You simply then remove the compressor fuse & you are good to go.