"Our target customers are those who like LONG online discussions. Where can we find them MOST of the time?" What's your answer?

You have kind of answered your question. As your target audience is online most of the time, you should make use of various online media to target them. Try to figure out how they access the interenet, through laptops or ipads or from their smartphones. Based on this info and their internet behaviour, target them through social media, mobile apps etc. and direct them to your website for filling forms and creating leads. Try to reach out to them through emails after they have shown some interest. 

You can find them on Social Media Websites.