Trans FLuid G

 I have a 1983 Jaguar XJ6 with a Borg/Warner 66 automatic transmission.My owners manual reccommends using type G trans fluid. I  have never heard of this type before and I cannot find this type fluid anywhere. Can anyone tell me where I can find this type or a equivalent ?
 
 Thanks !

Dexron III will work just fine. I wouldn't mix it though.   I'd drain the old out and put all new fluid in, along with a new filter, just to make sure.  Sure can't hurt, and may need it anyway. 

Thanks ! I appreciate the info...I could not find any information on this anywhere but here !