I would go with this. I think this is the right part.
http://www.marcospecialties.com/pinball-parts/A-00627

You can remove the bluing with vinegar (15 minute soak) or steel wool.

For future reference, Game Room Guys has quite a bit of stuff, but also has the highest prices on everything.
Pinball Life, Pinball Resource, Marco Specialties, Action Pinball, and others are much less expensive.

The problem with blue steel is that it rusts very quickly, particularly with the blue removed.

Have you thought about having the part nickel or chrome plated?

I have three LOTR ramps that have some blue steel flaps. I sent the whole things to Ron Woodard for plating. You might be able to mail the flap to him and have your flap cleaned up and plated for very little money.

Had I not gone that route, I would have probably bought something like this to figure out the optimal thickness and replicate the flaps - https://www.amazon.com/Stainless-Unpolished-Finish-0-001-0-020-Thickness/dp/B002BX3USS/ref=pd_sim_sbs_328_3

If you can't find someone who sells the ramp flaps you can make your own. Just use regular spring steel instead of the blued stuff.

http://pinballrehab.com/1-articles/pinball-restoration/ramps-and-plastics/136-making-ramp-flaps