The 245/50/16 will be easy to get and will be available for a long, long time since it was also a standard IROC Camaro tire size. The larger 255/50/16 will be similar since it was standard on '84 to '87 Corvettes. This is a good thing since other sizes are getting scarce as time goes on.
The 215/50/15 is the one that will give you the most headaches in locating as very few still make this size. I have seen some people go to the more readily available 225/50/15, but it does make the front look a little tall on some Esprits.
I have also heard of people going to a 55 series tire as an alternative by going to a lower initial number and higher in profile to compensate, but am not sure what size they used. 195/55/15? Something like that. Hopefully others can give you some good options.
Roy