pentax MZ3 lens button is gone, please help

ive got a MZ3 and the button that releases the lens so i can change the lens is gone. The black button on the lower left side o nthe body. Anyone who knows were to buy a new one? Its a silly thing to loose but i dont find any place to fidn a replacement since these bodies are sold cheap on ebay.

any thoughts and help?

My suggestion would be to contact Pentax customer service, giving details of the missing part. They will most likely send a schematic drawing of the camera, from which you should be able to identify the part number.
You then have a choice of sourcing from a camera specialist or direct from Pentax.

Alternatively you may find that the part is common with other MZ series cameras and it may be cheaper to buy a non working camera on Ebay for spares