Networking - If you want your list numbers jumping by hundreds a day start networking with the "right" people.

"Send an email reply when you get quality content in your inbox, introduce yourself. get active on their blog with quality comments"

There is nothing that get's your list numbers jumping like a wagging tongue. When people are talking about you in a very positive way all over your niche, then you know you've made it.

N.B it's no fun getting loads of grovelling email every day so networking with the right people may take a while. You have to always consider "why" should this person of influence give you the time of day..?

... What's in it for them?

Always get bust knowing that to network well you have to offer value for nothing that way you become an asset and an asset can always slip in the ood request.

Brain storm a few things you may be able to do for the top guy's in your niche. Again don't underestimate your worth and think outside the box growing your ideas.

Free articles, forum question fielding, finding a really great back-end offer for their funnel, suggesting and even contacting quality list swaps for them.

... Offline Clients?

Find an affiliate offer for an offline business their list would love...
...Then you helped them draft an email as only we online marketers can, and blast their list.
Would you be valuable to them?

Forums - Search google for your niche keyword plus forum like this. "kite+forum" including the quote marks. That will give me a list of forums where they are interested in "kites" Forums are a great way to fins subscribers for your niche subject.

Most forums will allow you to add a signature link that gets displayed when you interact with the threads (leave a message/answer)

Make sure before you sign up to your new found forums that they have an active membership with at least a few hundred members. Look at he forum threads, check the dated of the posts and most importantly check the answers from other members and see if they have signature links in them.

Has the "authority forum member" in the niche a website that's optimized in their signature link? Every forum has an avid fan member poster, some have no idea about affiliate marketing...
..You could offer help in that area for Kudos & brownie points & profit!

"No signature link allowed, scrap that forum and look for another"

Try variations of your keyword if you don't come up with enough forums. 2 or 3 in your niche are more than enough if they have high numbers and active members.

The more value you add the more subscribers you will get. Your forum responses remain online as long as the forum operates so make your threads great and thought provoking.