Are their adapters for nikon lens to sony dslr cameras?

I recently purchased a Sony a57 dslr camera and I want to buy new lenses. The lens that I was looking at was a 55-200mm lens but they discontinued that certain lens for Sony. I looked around and found that Nikon has a lot more to offer in the lens department and they had the certain lens that I was looking for. So my question is if there's an adapter that allows Nikon to merge with Sony cameras?

No, but you can save money by buying used Minolta AF lenses from a reputable dealer who includes a warranty.

Also, just because a lens has been discontinued, it doesn't mean that dealers won't have it in stock.

Get the Sony 75-300 f/4.5-5.6 if you want a telephoto… Better lens and costs less than the 55-200.

Or, as pointed out, look for Minolta auto focus lenses, which will work just fine on your camera. The 70-210 f/4 is an outstanding piece of glass, and cheaper than anything from Sony.