The best way to go about obtaining a list is to build your own. I have never purchased a list nor would I ever consider doing so.
In order to build a list, you need a blog or some sort of site that you can offer valuable information in exchange for a name and email address. This can be in the form of a free ebook or video series, a newsletter that delivers quality information that will help your subscribers.
It takes time to build a decent size list and you have to make sure that you are giving your list something of value to build up a relationship. You do not want to build a list and then throw offer after offer at them.
This is not something that you can do overnight. I have been building my list for a little over four years now and I only have a little over 15,000. I treat each and every one of them as if they were my best friend. I offer quality information and answer all the questions that I can for them. If I can't answer the question I point them in the right direction.
There are other ways to promote affiliate products. As you are promoting products with a landing page and/or blog, you have an optin box with an enticing offer to grab their information. Once you have them on your list you feed them with information and then throw the occasional affiliate offer at them.
Just remember, as you are doing this, treat them like you would your friend. Only offer products that you truly think are quality and will help them. Don't try to use your list as an ATM. They can unsubscribe just as quick as they signed up.
So, build your blog or landing page and start building....