Realsimulation probably holds most of them. A number have been made specifically for RUb, e.g. my "ASW mod".
You can also take the RUb download and pull out files from there, but you have to know what is what. Fortunately, I think the readme notes what the changes are and where. Still, it helps to be familiar with the data folder structure, something that only comes with the (monotonous) experience of digging in that folder all the time.
It's a hassle, yeah.
To note, I've not actually pulled RUb apart - for what I currently use, I just took RUb 1.43 (which I helped develop) and added/changed things in it to the point that it's completely unrecognizable.