One method is probably to target the sites that you want to obtain links from and contact the site owners. I get get e-mails with offers to purchase links like that on my sites almost every week, but I ignore them because I do not sell links. Make a reasonable offer for the links.
Make sure that the links are contextual and are embedded in similar articles. The links must look natural.
I have never met a link builder who provides quality links, so it may be a waste of time and money to pursue that channel.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin