Are there any AirPrint compatible print servers?
Lantronix xPrintServer is a hardware device which can be plugged into your network to offer AirPrint services to iOS devices. I haven't used it myself, see ArsTechnica for a brief description:


  Simply plug it in to your home or office network, and every printer accessible on your local subnet—be it wired or wireless—will now show as an option when using AirPrint. There's no configuration necessary; any printer that supports JetDirect, LPD, or IPP printing will work, and that includes pretty much every printer with network support.