RDAT files were originally git-LFS-tracked here, but GitHub Pages does not transparently serve LFS objects (it returns the LFS pointer text instead of the file). All RDATs now live as assets on the data-v1 GitHub Release:

https://github.com/DasLab/rmdb.github.io/releases/tag/data-v1

The detail page for each entry links there directly. To download all RDATs in bulk, see the Release page assets list.