A/C Refrigerant oil

I have a 2000 Eclipse GT bought it used. The weather is getting hot and humid, so my AC starts acting up. The car has 129K I know the AC needs to be serviced and charged. I am a certified MVAC tech. In the Eclipse bible it says that the system requires a Sun PAG 56 oil. Dealers don't carry it and I can't locate any from my sources. What's the deal.

I'm thinking the PAG 56 is a viscosity rating? Can't you just get the same viscosity but not in the Sun brand?

PAG OIL
Definition: A type of polyaklylene glycol lubricant used as a compressor oil mainly in original equipment R134a A/C systems. Various viscosities of PAG oils are specified by the vehicle manufacturers for specific A/C applications.