If you know who they are, specifically, just call them or e-mail them. Say something along the lines of: "Hi [their name], you don't know me but I came across

If you know who they are, specifically, just call them or e-mail them. Say something along the lines of: "Hi [their name], you don't know me but I came across your name on [LinkedIn / their site / industry site], and was impressed by [whatever made you want to call them]. I was hoping to get your advice on a service I'm creating for online ad agencies, would you be interested in meeting up and chatting about the industry? I'd be happy to take you out to lunch sometime this week." Be prepared to answer follow-up questions about the kind of service you're building. At the meeting, I wouldn't ask if they'd buy it, and if they say no, ask what their reasons are (it comes off as defensive, and potentially overbearing). I'd discuss the service, then ask first: "Are there any problems you see with my sales strategy? Any reasons an agency like yours wouldn't purchase it?" I'd also ask what the biggest selling points they see are, and what they think you could do to make it even more marketable (note that the answers to this question are often not actually in your best interest).