In all matters involving any financial issues, for instance post judgment proceedings for Modification or Contempt, both parties are required to file full & complete financial statements & provided a signed copy to the other party. If you are unable to obtain the other party’s financial statement, file a motion to compel with the court. That motion will be granted and the other party may be sanctioned or ordered to pay your attorneys fees for drafting, filing and presenting the motion. Keep pressing, you are entitled to the information.
The first attorney's advice regarding financial statements are what's called a 401 disclosure. 410 disclosures are not required for child support modification cases. There are other ways to get what you need though.
Particularly where finances are at issue (chlid support), you are entitled to these documents. The quickest way to get them is to file Requests for Production of Documents. If the opposing party does not properly respond, then you can bring motions to compel.