There is no guarantee you can actually get them back. It is kind of hit and miss. Especially when it has been so long.
Did you check your google account to see if they were possibly backed up there? If you have the account to auto update/sync it is possible they are.
Barring that, the only other thing I would suggest you try is software that can search the device. But again there is no guarantee.
There are actually a few apps/programs out there that "may" be able to help you recover the data.
A few of the programs you could try would be... DiskDigger, MobiSaver, Android-Recovery and Tenorshare. They are all data recovery apps/programs. There are many others out there, so check around and see which you would rather try.
One...