You say that a police report was previously filed alleging theft. Contact the police report with your allegations and ask them to investigate. You also could try contacting David Hall, co-founder of Professional Coin Grading Service, who reportedly authenticated the find. You could also try contacting David Kagin of Kagin, Inc. who is reportedly representing the couple that found the coins.
Obviously, you will need to be able to back up your claim that the gold coins belonged to your Aunt with documents and photographs.
You also mention that the coins were covered under her homeowners' insurance policy. If that truly was the case, it would seem that the insurance carrier would have already paid out on the alleged loss.
***This response is provided solely for general information purposes and is not intended as legal advice, nor does it create an attorney-client relationship.
Not sure we can help. But, if they are being sold on Amazon, you can report them stolen along with your police report. The vender, if located in California may, and I mean may, be subject to Cal Pen Code on Misappropriation of stolen property. The vendor could tell you the name and identify of the buyer, which the SF PD may need to assist you in.
Now, as for coverage. Stolen property should be covered in your Homeowner's policy. Make a formal claim and get them to cover, or provide you a detailed basis of why its not covered. Gold Coins should have been disclosed previously on your policy along with other major personal items (eg. Jewerly, ) and had them appraised. Otherwise, your claim becomes challenging.
This email does not create an Attorney-Client relationship.