Did you try Pinball Resource?
I know he has some of the back panels, and he had the red balls at one time (used on other Gottlieb machines). pbresource.com

Looks like he's out of stock on the back panel. You'd probably have to call or email and ask about the balls.
I can't locate them on his website.

Hey JR,

Do you know how many balls of each color should be in the machine?

If you have the balls but they’re really dirty, they’ll clean really well with novus 2.

Six white, six red.

Thanks, I just checked a project machine I have, 9 white & 1 red.

Looks like I need some balls.

As someone mentioned above, you can get them pretty clean with Novus 2 polish. I'd maybe give them a little bath in dish soap first though, if they're really dirty.
Use a toothbrush and scrub them. Dry them thoroughly, then use the Novus. There's a thread here for EM parts wanted. Post there, and someone should be able to come up with what you need.

Speaking of those 12 balls, have you ever gotten all 12 across in a 5 ball game?

Answer: No!

It's near impossible, though not. There should be some sort of super special for that achievement. This game is criminally underrated.

I never did. Racked ten a couple of times, and eleven once.
I've had three copies of this game. I took one of them to Pinfest a few years back, and a friend of mine who is a very good player, did it on his second game!
It's the only time I've ever seen it done.

If you start with alternating red/white balls, you'll see that they get juggled around, and don't stay that way. So, no. Just drop them in there.

Is it possible to get a plastics set for Bowling Queen? I have a full set on a machine I am working on, but some have small edge chips on them or have been repaired at some stage.

Unfortunately, Pinball Rescue in Australia ceased trading a few months back so such plastics aren't available. I have read on this site though, that Shay Arcade might be getting involved in plastics so keep an eye on their website for any updates. Might be worth a shot asking Steve or Jimmy at Pinball resource to see if they can help because they stock some plastic sets.