Here's a few things to look at in the order I'd try them, but depending on your budget you might buy the used unit early in the process.
1. Figure out exactly which metal pieces are worn
2. Call the usual suppliers and ask if the part(s) you need are available.
3. For parts that aren't available, decide if they can be repaired of fabricated.
4. Buy this used unit
ebay.com link: SS Bally NIGHT RIDER Pinball Machine 5 Bank DROP TARGET used pinball parts