I could not find trek bikes at target or walmart type stores. From where I can get trek bikes? Are there any other brand names for bike which are good?
Generally Trek bicycles are not available in department stores. Ocassionally some gray market Trek bikes will show up at discounters but other than that the only way to buy a Trek is to get it from a Bicycle shop that sells Trek bikes. Trek won't honor the waranty of any Trek bike not purchased from an authorized Trek dealer.
There are department store bikes and there are bike shop bikes. Department store bikes are cheap, usually have low quality parts that quickly break or malfunction under hard use, and are often poorly assembled and adjusted. Bike shop bikes are more expensive, higher quality, and usually assembled by well trained and experienced bicycle mechanics. There are a few sub-par bikes in bike shops and not every bike shop has good technicians but in generally you are better off dealing with bike shops than department stores or discounters if you plan on riding a lot.
One of the things that muddies the waters is Schwinn. Schwinn historically has been a high quality bike that was only sold through bike shops but since their bankrupcy they have been selling bikes in department stores. Consumers assume that these Schwinns are the same quality of bike they grew up with but they really aren't.
There are lots of good brands of bicycles. Trek, Canondale, Giant, Fuji and GT are a few good brands but there are plenty others. In general any brand of bicycle sold in a bike shop is a good brand though there are differences between brands that may make one work out better than another for you. The best thing to do is to go to a bike shop and test ride every bicycle in your price range and choose the one that rides best.
I'm partial to specialized bikes myself - I had a specialized rock hopper some years ago, no shocks, but carbon fiber components for some bits, etc, and it was a great ride. Sigh. I still miss that bike.
you can buy them online. Google.
go to ebay.com