Sorry if this has been asked millions of times before, but is there a place where I can find a "big" XR_interior1 file?

Working on my first interior now, but need better quality to make it good...

I don't think you can find an "official" high res one unless you steal someone else's and use that as your starting point. What I do is just convert the original to a higher resolution (1024x1024) and just work on that.

try www.lfs-database.com