First off welcome to the forum.
If you are just getting started in model building or collecting, take some time and analyze what really appeals to you most. It could be cars, trucks, airplanes, boats, or other subjects, and they all come in various scales from tiny to huge. In addition to the building phase, you need some place to display your completed treasure(s). In general, plastic models (especially car models with clear plastic windows) don’t like dust. Over time dust clouds the “glass” and dulls the paint, and are best kept in some type of display cabinet. Models are also hard to clean without risking damage to many small components like mirrors, handles, etc., so consider what you will do with them once completed.
I’m in my 60’s now and have been building models since I was about 5 or 6. It can be a very rewarding hobby, depending on enthusiasm and dedication, and may require a lengthy investment of time and experience to master various building skills. Model building can very be expensive especially if you buy things on impulse so research first and buy on decision instead of emotions. The hobby can be relaxing and satisfying, just guard against allowing it to become more work than fun.
I’d recommend visiting the manufacturer’s web sites and review the various offerings to see what appeals to you. For starters try Revell/Monogram:
http://www.revell.com/
Real hobby shops are far and few between these days, generally don’t last long, and by necessity have to charge so much for their limited selection of kits as to make them not affordable. When I was a kid hobby shops were like the ultimate toy store, but today there are too many other distractions for a real brick and mortar store to remain profitable.
There are a few internet hobby shops that cater to the vintage model crowd, but even some of these have gone away over the last few years with economics being what they are.
Here are a few online places to check into for ideas of what is available or to purchase:
http://www.spotlighthobbies.com/
http://www.fantastic-plastics.com/
http://www.hobbylinc.com/prods/s_amt.htm
http://www.bobspromotionalcars.com/ (mostly preassembled promotional models)
http://www.edeuce.com/ (1/8th scale cars)
And if your interest turns more toward collecting than building, there are quite a few die cast providers including these:
http://www.franklinmint.com/category...FRATbAodCG8Jxw
http://www.danburymint.com/diecast/?...t+diecast+cars
If plastic kits turn out to be your main interest, and you want to continue building a collection, you’ll almost have to embrace eBay at some point. There is no other source that has so much to pick from at prices that are set by market demand, instead of a collector’s opinion that his stuff is worth a fortune.
Older stationary stores and some art supply stores like Michaels use to carry models, along with small town drug stores and dime stores. Most are now gone or have very limited kits frequently priced well beyond reality. Once in a while you can find a bargain if you develop a passion for the hunt. If you're looking for a model of a specific truck or vintage vehicle let us know, or feel free to shoot me a PM.
I hope you find this an enjoyable hobby. You might also want to take a look at this site. They also have an excellent forum to pick up ideas:
http://cs.scaleautomag.com/scacs/forums/