Metal injection molding uses pellets made of plastic binder and metal.

These are injected into a mold. Then the product is sintered to produce a 100% metal part.

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Using avilable MIM pellets - one should be able to convert these into 3D printing filament using a filament maker.
If the binder is polypropylene, the filament can be printed in a high temperature 3D printer chamber.
The part produced can be sintered to get a 100% metal part.
Thus, here is a way to generate 3D printing filament-based full metal 3D printing in any metal.
Others are already doing it - but not using filament - but pellets: Metal Injection Molding Pellet 3D Printing.
Also, Virtual Foundry is producing 3D printing filament from proprietary formulations of plastic, additives, and metal powder

Metal Injection Molding Pellets