To my knowledge, there are no online sources for radio codes, understandably enough to discourage theft. If no record of the radio code came with the car, then you have to go to the dealer, I'm not sure what if anything the charge might be, somewhere I heard $75, but certainly ask beforehand.
Not having any service records is a bit of a high wire act, particularly with a car like this that can invite "immature" driving and neglect of service and maintenance from a previous owner. Do as best you can to find out where and by whom the car had been serviced, to get some idea of where you stand. The less you're able to recover that data, the more you're going to have to establish a new baseline, including plugs, oil, air and oil filters, microfilter, complete coolant flush (radiator and block), transmission and differential oils, condition of control arms, bushings, and ball joints, brakes, shocks and struts, condition of battery (with winter coming). It'd be a good thing to pick up a Bentley manual, it's rather thorough on what needs to be done, and how to do it.