Och! There's nothing to file a lien against. I would definitely get an attorney involved. A collection agency may or may not be the best route without a judgment already in place. If it's a LLC, you probably wont be able to seize personal assets, but business assets could be seized and auctioned off to satisfy the debt.
Not real sure how it works in NY state, but there is a reason its called Limited Liability. You may be able to go after personal assets.
For $40K, I'm seeing a lawyer.
I just have a ton of people who owe me $500 here and $300 there. Nothing that big in 1 lump.