How many grades of R22 refigerant oil are available.

Up to 6 depending upon where in the world you live and what temperature the system is running but the main R-22 lubricant is a mineral based oil and some of the newer synthetic styles are also compatible for lower evaporator temperature usage if care is taken since the newer synthetic oils can cause a problem with oil return from the evaporator..

You will be better served by using Google as a search engine since there are 100's of pages on the subject of R-22 oil and its usage.