Why is this so complicated?
A .pst file is local. It is backed up every night to a server. The server replicates to another server.
If this technology didn’t exist in 2009, then it is backed off to tape and stored for whatever the retention period is.
So, ask for the backup. If the government fails to produce that, subpeona every IT person and the data center entry logs.
I have no idea why in tarnation you posted that to me?