Limits to Exclusivity Agreements

I want to introduce plastic and tire recyclers to buyers in Mexico. I know some buyers, so it is a service I can provide, and I'd like to charge a commission like $1 per tire. Can I write contracts that will make me the exclusive representative of a U.S. recycler with Mexican buyers? How long can I define the exclusivity for? Does commercial law limit that kind of thing? If, say, I signed a contract with someone making me exclusive rep for 5 years, would the courts honor that?