Congrats on the game. I think any of these parts will replace the drop down target you have.
http://www.actionpinball.com/parts.php?item=545-5533-01-MON
https://www.marcospecialties.com/pinball-parts/545-5533-01
https://www.pinballlife.com/sternsegadata-east-rollover-drop-target-white.html
https://www.ministryofpinball.com/en/data-east-sega-stern-drop-target-545-5533-01-7291.html