What is it, and where do I get it?

I get mine at Ace hardware. Wally world might have it.

What is it? I let someone more qualified answer that .

Dissolves super glue, evaporates rather quickly, carcinogen. That much I know.

Would the archery shop have it, since its used with making arrows alot?

You can get it at Lowes, home Depot, wallmart etc. Look in the paint/solvent dept. If an archery shop did sell it, they would probably charge and arm and a leg. It's easy to find really and inexpensive.

i'm not using it, and i haven't figured out anything i have to use it for that i can't do another way.

It is used in auto body repair an aweful lot. It's about the only thing that will clean the wet, sticky fiberglass resin off of tools and your hands.

Dairy--be very CAREFUL when using this solvent--I have 'stupidly/un-intentionally' removed the screen print from my Liberty limb using this stuff.
It was attempting to clean the limb to install a (SVL) limb saver--I also removed my 'LIBERTY Screen Print from the outsider side of the limb as well. DUH!!!

What are you going to use acetone on?

YES , Not recomended for cleaning fiberglass limbs , it could weak'n them and cause a failure . Be carefull , its powerfull stuff .

If you are cleaning off an aluminum arrow to refletch , you should be allright , but take your nocks out and reinstall when dry before fletching , Id bet acetone will melt nocks .

Yip acetone is powerful stuff allright. It will definitely affect your nock. In fact 90% of all polymers will be affected by it. I personally wouldnt bring it anywhere near my bow or accessories. I would use an alcohol based solvent instead, similar to alcohol swabs used in the medical industry.
The other fact you need to know about acetone, depending on the concentration, is that it evaporates very quickly and fumes can transfer flame up to 30 yards in closed areas. Nail polish remover is about 6% proof and is a lot safer to work with but has all sorts of other additives, so I wouldnt suggest this either.
IMO alcohol swabs are the way to go, small, compact, economical, you dont need a cloth and it wont spill