If the printer doesn't support AirPrint, then unless the printer manufacturer provides an app (if they do, such apps are often quite limited), the only way to print to it is via routing the print job through a computer. If you have a Mac, look into Printopia. For a Windows system, try this:
You might also check out the Lantronix print solution. It acts as a gateway between AirPrint enabled mobile devices and non-AirPrint Printers. AirPrint relies upon mDNS Broadcasts, so your wi-fi access points and controllers need to be set to locally allow this traffic to pass through.
If your router happens to be one of the supported
Netgear routers, you might wish to check out the newly released
Genie from Netgear. http://www.netgear.com/landing/en-us/netgear-genie.aspx
Some routers offer a USB port which may allow you to connect a USB printer
to the router and print that way. My current printer offers both USB and wifi
connection so you may already have USB on your printer.
If none of the solutions from previous posts satisfy your needs, please
post back with the name and model numbers of your printer and router
so someone can offer further assistance.