Write to each of your competitors, explain the situation and ask for a referral to their lawyers. You'd be surprised how many are more than willing to make a referral against a troll Also search around for any other attorneys who have filed against this troll and contact them as well. They should all be willing to do an initial call for free.
You are trying to find an attorney who has a successful blueprint for dealing with this particular troll, ideally this particular claim. If the attorney is able to leverage their prior work or knowledge, your costs are greatly reduced. Also, if the troll has unsuccessful experience with a particular attorney they may just give up. Good luck!