Hi Anne

...
Have you tried requesting his records from NARA? If there's a next-of-kin still living (you mom/dad, aunt or uncle, etc.) you can request them through the eVetrecs system.
In all the records I've requested for genealogical purposes, I've found the best thing to do is just request the DD214 and then in the "Notes" box, enter the additional records you would like. I would think entering something like 'assignments and reassignments', 'unit orders', or maybe 'promotion orders' might work. It's better the more specific you are...
Have you searched your grandpa at ancestry or footnotes? Sometimes a newspaper article helps and sometimes ancestry can be helpful too when it comes to military records.
Do you have your grandfather's birthdate? Do you know where he lived? I'd be happy to help if you need it and good luck