You can go to ClickBank and look for support related offers.
Contact the people behind those websites because most of them collect emails on their landing pages.
These people should be your first priority.
They are not going to hand you their email list.
You need to either pay them or give something of value in return.
Another approach you could take that is probably going to be cheaper is to identify glogs that are in your niche.
You can do this yourself or you can hire a virtual assistant to do it regardless of your need to do quite a bit of research.
Find those blogs and then filter them based on whether they have the mailing list or not.
You also need to add another filter.
You also need to determine whether they get a lot of traffic.
You can do this through their Alexa site score.
Keep in mind that Alexa is not terribly accurate, but at least, it prevents you from taking wild shots in the dark.
Alexa can give you a rough approximation of how much traffic they get.
Filter your list of glogs or websites with email lists based on traffic volume.
Do not waste your time on websites that get very little traffic because chances are good that their lists are very small.
Once you have the list of websites to approach, you need to negotiate with them to advertise on their mailing list.
This refers to solo ads.
This is where you can get a pure list of people who are interested in your niche.