Finding PM's past the ones at the bottom of the user PM list

There is an old image that i sent around june/july of 2017, that i'm looking to recover. Unfortunately, the bottom of my PM list goes back to September of 2017. I know I've sent PM's far before this date, but they seem to disappear after a bit. I've gotten the data dump for my account, and it's too convoluted to efficiently search through. There must be a better way to find my past PM's.