You can datalog with the stock NB. It will take you a long time to dial everything in.
You can buy a wideband sensor from any variety of sources. You will need a wideband controller as well, however. The system most commonly used by Buell riders is the LC-1, which frequently comes with a WB O2 sensor.
The beauty of the LC-1 is that you can set it to emulate a NB signal, so that when you're done tuning, you can turn correction back on and set the LC-1 to pretend it's a NB signal. Or you can put the NB back in and sell the WB to offset costs.