It's written in the paper (Rodriguez-Gomez+ 2015) that there's merger trees for FoF groups but I couldn't find them on the website. Where I can find them?
There aren't any merger trees based on the FoF halos, they are always based on Subfind subhalos. What is described in that paper is a post-processing step, whereby the merger trees of "central subhalos" (i.e. halos) are corrected for fragmentation and then only central-central (i.e. halo-halo) mergers are considered, to make a "halo merger tree".