I see a point of diminishing returns, when sanding above 1000, if subsequently buffing. Even a quick light buff will erase all 1000 grit scratches.
If you really want glossy, and none of the above gets you what you are envisioning, or you find sanding up to 2500 to be too time consuming, you could try super-glue finishing the entire handle. That'll get you a high gloss "clear-coat" or gunstock look. There's a good thread about it that Bruce Bump did years ago, if you search. I don't often use it because I frankly don't like the plastic feel of a stabilized handle with that type of surface. If you look at some of Michael Rader's mind-bendingly pristine handle finishes, superglue is what he uses, too.