* The university of Waterloo has an ftp directory full of them:
http://links.uwaterloo.ca/Repository/RAW/
These are not "RAW" images out of digital camera. Too small.
"RAW" images cant be recognized from the extension.
The extension is e.g. "ORF" for Olympus, "CRW" for Canon and so on. Each camera vendor has its own proprietary raw format and file extension.
"Raw" images contain the original undeveloped (raw) sensordata, uncompressed or lossless compressed and are very large.
The size is commonly 10MB and no limit up.
You can get raw files from camera review sites for example here:
https://www.dpreview.com/reviews/olympus-om-d-e-m1/16Select "RAW" instead of JPEG, then the file is offered for download.
Most cameras have been tested and are available.
It should be said, raw image files cannot be simply converted and loaded.
They must be deconvoluted and processed before they are visible.
The colorspace of the physical camera sensor must be converted to the target color space (commonly sRGB or AdobeRGB) of the image.
Noise must be removed. Dead pixels or unusuable pixels (for phase detection) must be interpolated.
Possibly geometric distortion and chromatic abberation of the camera lens must be compensated. (DCraw and most open source raw converters dont do this automatically. For this you need a commercial converter, probably these read the maker notes and this content is under NDA and not freely available, it must be reengineered)
This is not a straigthforward process. There are a lot of steps where parameter adjustments and decisions must be made which are not fixed, but are a matter of the skills and taste of the photographer.
It is probably better to use an existing tool, because photographer who use the raw format of their camera will probably want to use their preferred tool for raw development.