Q: Can i purchase hardware to make my existing printer an AirPrint printer?

No

As Allan says above - no.

But since you're willing to purchase such hardware if it exists (which it does not), you might consider purchasing a new AirPrint capable printer.  Not all AirPrint printers are very expensive.

There is software.  It's called "HandyPrint" (from Netputing.com) and it allows you to print on legacy printers that do not support the AirPrint protocol.  It is compatible with OS X and iOS devices.  There is a trial period and then if it works for you, they ask for a $5 donation.