How can I naturally shine my kitchen granite counter tops?

Are you sure they aren't made like that. The new granite style is honed, not to be shinny, and more exspensive. You can get granite sealer with enhancers that would add a little shine.

I'm not a pro, but I have cleaned up a bunch of counters as a flipper. My guess without seeing them is they probably need to be resealed. You can tell by sprinkling some water on the counter, if it beads up the seal is fine, but if it soaks right in, you need to reseal. Do the test in the parts of the countertop that see the most use, most of the time the seal near the walls lasts forever, while the edges you work on wear away. Fortunately sealing is a relatively easy process, Here is a link to a product I have used and like, but there are other products you can use.

To keep it shiny be sure to use the right cleaning products, if you use acidic products you can actually etch the surface of the stone. If this has happened the stone can be repolished, but in my experience this is a job for a professional, I suppose a homeowner might be able to do it, but the investment in tools is substantial, and getting the right feel takes experience most people don't want to gain on their own counters! It's a bit pricey, but it's much less expensive than paying a pro to try to fix your mistakes.