Answer:
You will probably not be able to find any used heavy duty plastic pallets. Heavy duty plastic pallets are relatively expensive and those companies that use them often buys them back from their costumers.
But if you aren't in a hurry sometimes smaller companies get one or two that they don't need. But since they only got one or two they will likely only throw them away and not sell them. Therefor you'll have to call or email to different companies and say that you are interested in heavy duty plastic pallets if they ever get any. Or you could post an ad in your local newspaper or on the Internet.

if you are interested in buying new heavy duty plastic pallets you should probably check with more than one company before you order any. Since they isn't as common as other kind of pallets you could save a few $ by looking around.

Searching the Internet for "heavy duty plastic pallets" should get you to some companies. Some times these companies won't be in the top of the search results so you will probably find allot more if you go trough several pages in the search results. You could also look for advertising from the companies.

Answer:
It depends on what kind of pallets you got. If your pallets are made of paper or soft wood you probably wont be able to sell them same if you got pallets that are in non-standard dimensions.

But if you have pallets in real wood, plastic or even metal there shouldn't be any problem to get rid of them and make a little money. Some pallets, EUR pallets for example, are always easy to get rid of. Try talking to a local transport company.

If you are in no hurry to get rid of the pallets you could always place an ad in your local news paper or on the Internet. Or you could try to call some local (small) company and you shouldn't have any problems with getting rid of your pallets.

There are also often companies that are looking for used pallets trough ad's, keep your eyes open!

Answer:
If your pallets are in good condition you shouldn't have any problems selling them. Try calling some local companies that you know are either transporting goods or selling goods. Selling used pallets to companies that will use them to transport the gods they sells only works if it's a small company. Larger companies will use new pallets, or at least not bother with buying a few used pallets at a time.

You could often find people near by who wants used pallets, try looking for ads in the newspaper or on the Internet.

If you got the pallets from a company that sold you something and transported it to you on the pallets you could check with them, sometimes they are interested in buying their old pallets back. Again it's often easier with smaller companies.