I know that Reaper comes with two or three different count ins, but those can get boring fast. I personally downloaded a big set of drum samples. It was too long ago to remember where or what it was called, but searching for “drum samples” on Google may give you a lot more to work with or a lot more to add to this count in pack you’re planning.
You are about to leave Rhythm Gaming World and access the external songs DB. While no song or file sold for commercially available videogames is hosted there and only fan generated content is allowed, Rhythm Gaming World has no direct control over the database and no files are hosted here. Alright, we had to made you aware of this, now you can visit the database!