I hate to break it to you, but many MIR records sections are understaffed, overworked and severely backlogged. What you are describing is called "informal access", and they are under no obligation to provide it in a timely manner, or at all for that matter. You'll note that the OP mentioned that he was told he would have to wait 4 to 6 months. He also mentioned being on a PCAT, which means he's still serving.
The ATIP process does have set time limits for providing you with the information you've requested. That said, if they are backlogged, they will request extensions if you are not in a hurry for the information - but as I mentioned, if you are seeking the information for a VAC claim or other legitimate reason that requires a quick turnaround, the ATIP people in Ottawa are very good at getting the files to you in a timely manner.
FYI, this guidance comes from DAIP themselves. I think they're in the best position to advise how to obtain your records.