The plungers are quite hard to find on their own. Here are some for sale, These are the same as the plungers used in an EBD. You could ask the seller for more if more are needed, he's a good seller, he will help if he can, or you may need to buy a complete assembly to get more of them.

ebay.com link: Bally Pinball Target Reset Kicker Plunger Armiture 70s 80s Games Good

The Bally knocker plungers from that era are similar, but not a suitable substitute as the knocker plunger is shorter than the drop target plunger.

There have been a few trials to get these bell posts made but the tooling costs have just been too high or the other methods and costs are too high, like several dollars each even if bought in 10k type bulk, at least for now. Too bad really, would like some of these parts to be back on the market.

Try soaking them in Rustoleum?

do you mean evaporust?

Maybe it's time for a complete color change (like green or red). Paint the spacers, change the post color, and order colored silicone rubber rings to match. Just don't use colored LEDs for GI.

https://pinside.com/pinball/market/archive/17835

You can make decent replicas out of aluminum thin-wall tubing and a flaring tool

Your local hobby shop will have thinwall aluminum and brass tubing.

345_Flaring_Tool_72dpi_(resized).jpg

HF has one for $18, but I've never tried it:

http://www.harborfreight.com/double-tube-flaring-tool-kit-66534.html

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Heat the tops with a soldering iron to remove them from the plastic. It doesn't matter if the hole gets too large to hang on to the top of the spacer...the screws will do that for them.
Use a bench grinder stainless wire brush to knock off all the crud.
Wet-sand them with 200, 400, 600, 800, 1K, 2K, and 3K grit.
Run a final polish of Mother's Mag Polish on 'em.
Probably should shoot them with a light coat of clear to reduce surface rust in the future.

See if that don't make them shine up enough for your standard for this title. Take some pics in progress and before/after comparison. I think you will be pleasantly surprised.