Often your only choice is to make your own compressor reed valve, if that is the part that has failed on your air compressor. A common failing on lower cost air compressors, for sure.
Making your own will require a bit of work. It helps if you are handy with tools and enjoy DIY crafts.
Like almost any new project, the first time you make your own will take much longer than if you were making your own compressor reed valves all the time.
Once you have torn down your compressor pump find the valve plate.
There are many shapes and sizes of reed valves and compressor valve plates, so don't be concerned if yours is different than the image shown.
You can see that one of the "fingers" in the reed valve that fit over the ports has broken off. This is not an unusual occurence due to the high heat inside the compressor pump, and the thousands and thousands of cycles the reed valves go through.
So, now it's time to make your own compressor valve plate.
Another approach is to purchase high carbon spring steel shim stock. Get a supply that is as thick as the original valve plate from your air compressor. If you perform a Google search using the phrase - high carbon steel shim stock - you will find a number of sources.
Regardless of your choice in reed valve raw material, just make sure that the material you select is one that remains flexible over thousands and thousands of cycles and is heat resistant. Otherwise, you'll be tearing your compressor pump down again and building a new valve plate for it sooner rather than later.
Using the old valve plate as a template, mark the new material with the correct shape.
Use a scroll-type hacksaw to cut out the valve plate shape from the new stock. To make cutting the thin spring steel easiery, consider placing the shim stock on a thin sheet of wood first, to provide a base for cutting and to reduce vibration as you cut the spring steel.
Drill comparable sized holes in the new valve where they were in the original plate.
De-burr the new valve plate completely to ensure that it's flat and no small spurs of metal prevent a tight fit over the ports in the valve pump.
Install the new reed valve plate in place of the old. But first... consider the gaskets.
Odds are pretty good that in the disassembly of the pump you may have damaged a gasket or two.
If you don't use new gaskets when you reassemble the pump, your compressor pump will not build pressure correctly.
If you cannot find a gasket kit for your compressor here's how to make your own compressor gaskets.
Reassemble the pump with new gaskets and your custom built reed valve plate, and your compressor and you are back in business.