The only option left is an executive order from POTUS that hits hard as feck against anyone owning any firearm other than a hunting rifle. When you choose to not take the carrot, the stick is the only other way.
As a precedent of a POTUS signing such an executive order that forces Americans to surrender a certain type of goods was FDR in April 1933, when Executive Order 6102 required Americans to surrender their gold (other than gold jewelry, gold coins, and a very small amount of gold bullion) to the government for payment of the then prevailing value of the gold surrendered. The purpose of #6102 was to prevent hoarding of gold that would have worsened the Depression. It was an emergency measure in short then, and thus we can use the same rationale for this kind of emergency.
People in polls HATE the way Joe Biden is taking on the current gun problem. I think most want him to swing the axe rather than rely on the same unreliables in Congress.