Not sure what state you are in, however I can tell you from the standpoint of Florida, and it's probably the same in your state.
What would have happened is there would be title agency involved in the transfer of the title of the property. Part of their job is a title search, which will show any liens on the property. Since that didn't happen, they are the ones liable, not the lender. There would be title insurance that would have been purchased during all of this, and this is exactly what it is there for - if there are any liens that got missed, the new owners aren't liable for them.
So what this will mean is that you could ultimately collect through that insurance. However, that also means that your ex-husband still gets the money he got from the sale. So you may want to contact the court and advise them of this.
What should happen is they should make him pay before turning to the insurance, however since that worked oh, so great the last time, you may have to go with the insurance. However, there is a possibility that your husband could face criminal charges since he got the money, but never paid you, and obviously never disclosed the lien during the sale.
A lawyer might be of help, but I would first start with the court, then call the new lender (public records are great) and tell them you are claiming your lien on that property. They should be more than happy to help after you show them the documents you have. They should get back with the title agency and go from there.