I work for a publication printer, and we buy mail lists occasionally. Like Jarrod said there are millions of list companies out there, and most will give you the same results. You should be able to put in certain criterias, for example household incomes, number of people, businesses with revenues of x amount, businesses with x amount of employees and on. Just make sure the list you are buying is NCOA linked which is the National Change of Address, that helps cut down on undelivered mail thus making your list more accurate. I would assume you are working with a printer, and if they are mailing this for you they should be doing the NCOA anyways and helping you buy the list.
Shoot me an email if you need any help i would be glad to help.