Depending on the types of trucks you are looking for, you can find trucks at http://www.penskeusedtrucks.com/. You can also find trucks at http://www.buyatruck.net/
If you are looking for big trucks for sale you can go to a yard where they sell semi trucks it just depends on how big you are looking to go you can also go to just a normal dealership.
Dump Trucks on ebay will be limited but it's definitely worth looking. You can also search at http://vehicles.oodle.com/used-vehicles/for-sale/dump-trucks/
If one is looking for bucket trucks, he should visit "CommercialTruckTrader". This website is used by several manufacturers to sell used and new trucks.
If you are looking for trucks that are for sale by owner, your best bet would be to check your local newspaper for any listings available in your area. There is usually a good selection in the classified section of your local paper.
If you are looking for a place to find used work trucks for sale try one of these: vehicles.oodle.com �ۼ Commercial Trucks www.traderonline.com/ www.truckertotrucker.com/trucking/ford-trucks.cfm IF you are looking to find out more information on a specific truck you could try: www.carfax.com for a vehicle history report.
You can check out the Craigslist in your area for trucks for sale. You can search by price, so you can find the trucks in your price range.
You can find heavy trucks anywhere from searching online to going into a car dealership/shop itself and looking around at different heavy trucks that they have available.
If you are looking for a new GMC truck for sale the best place is a local dealership in your area. If you are looking for a used GMC truck the best place to look is on Autotrader.
Chances are you can find exactly what you are looking for by looking on the website craigslist. There are many trucks available for sale online.
You can try looking on www.craigslist.org in that area for used trucks. You can also try www.autotrader.com for used trucks in and near that vacinity.
Truck Trend (www.trucktrend.com) lets you do detailed searches for the type of truck you are looking for. There are also good pictures of the trucks.