Now where do I find the bootloader for the 32u2 as a usb to serial converter so I can upload programs via the onboard usb rather than hooking up a usbasp programmer.
Inside the Arduino IDE development software, the bootloader can be accessed from the menu, Tools -> Burn Bootloader.
I used this video as a guide (despite the language accent):
In my scenario was a bit complicated by the lack of a programmer, so I ended up using a second functioning Arduino that was programmed with the ArduinoISP sketch.