There are more parts in the world than the KiCad library can encompass. It would be a larger task than the software and endless.
When people ask for a symbol, they may not be aware there are three separate things. 1. The symbol, which is an um, symbolic representation of the part, 2. The footprint, which gives the pad configuration and the 2D space it occupies on the board, and 3. The 3D model which adds the vertical dimension, and the look of the part on the board.
The first is usually easy to satisfy. In your case you just need a generic connector with 50 pins. Something like a 2x25 connector from the symbol library would do. Worst comes to the worst you could create one which is a rectangular box with 25 pins on each side.
For the footprint if you can’t find one or modify one from the manufacturer’s downloads, you could design your own, putting down pads in the right places, perhaps with one of KiCad’s footprint generators, and establishing a courtyard for the part so that you can see on the PCB editor how much space it takes and KiCad can detect collisions with other parts.
For the 3D model designing your own requires working with CAD software like FreeCAD. The realism you want affects the amount of work. This work is optional, you’ll just see pads in the 3D view if you don’t supply a 3D model.