Thats a great way to practice and learn - especially if you record yourself and listen back to it!!
I haven’t done this, but I hear you can take the Rock Band games and access the original files. There are also a bunch of songs floating around called “Multitrack Masters” that have the original files unmastered, so you can put them back together w/o the drums.
The legality of this is in question, though, although in theory if you are using it for educational purposes its legal.