Well, if they aren't showing on the phone, you might want to try and restart the phone and see if they show then. If not, try connecting the phone to a computer via USB cord and see if you can see in that folder (not using Samsung software to access it, but just Windows and open it as a folder).
If you still cannot find them, they may have been deleted when you deleted others. It happens. There is no guarantee you can get them back, however you can try the following...
There are 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. There is also one called RECUVA, that I have heard is free, which you could try.
One important note though, most of these programs are not free. They may say they are "free" or have "Free Trials" and "Free Downloads". Yet to actually recover your data, and get your files back, you may be have to purchase the program/app. Just so you know.
NOTE: For future reference, I really would suggest backing up your data to a computer or cloud. Often. Better to spend the time doing that, rather than to be out all that stuff if the phone dies, things get deleted/erased or it gets stolen.