Rogerthat1 - Based on what you described, the issue is actually with the clearing firm your broker uses (not your broker). I can't find any reasons why UNGS would not be ACATS or DTC elgible.
There have been several clearing firms/brokers that have classified stocks as Non-DTCC Eligible Securities, because of the pass through costs associated with trading them. One of the biggest in recent memory was Apex Clearing Corp, which was affiliated with Zecco. This allowed Zecco to charge a hefty amounts of money to sell or buy a stock ($150.00-$500.00 per trade).
I hope this is not occurring with your broker and/or their clearing firm.
My posts are my opinion only and should not be considered investment advice! Do your own DD!