I find signature link sales for many webmaster forums, any site for gadget related links for geeksbest
if you have a scaping/harvesting tool, you can put together a list by using the tools and custom search strings. another method would be just by doing simple google search and find forums one at a time. just find a few forums and pm a few regular members to see if they are interested in selling. you can also post on those forums with your own sig links