Harvey Vinyl Solid Core Storm Door hardware

I have a Harvey Vinyl Solid Core Storm Door. It has a Knob and Latch Hardware. As the knob turns on the outside to open the latch also turns. My problem is that the spring mechanism on the inside lact will not automatically return to the horizontal position on its own to latch again when closed. I need to fina a replacement for this inside latch or new complete hardware set as the door itself is still pristine. Please advise. Thanks