My current day job has me working for a Market Research firm. While I am not a market researcher by trade, I know we engage without other firms that will bring together a statistically relevant group based on market demographics. These groups are often compensated to gain the time of qualified participants. If you want to start with something less expensive than a focus group, Survey Monkey includes the ability to acquire participants for a survey based on demographics. We often use this survey approach when doing concept testing for other companies.
Hope this is of some help.