http://www.marcospecialties.com/pinball-parts/10-148-XX

They can also be ordered individually for $0.095 each.

Personally, I think the one in the game is appropriate to hit every skill shot. I suspect a stronger spring will make all the skill shots more difficult than they already are.

Mine also hits the "A" on a full plunge. I'm fine with that as long as it's consistent as I don't think I would be using less than a full plunge to try and hit a different letter anyway.

I would prefer the game play to my liking than have the plunger hit the DWARF letters a couple letters up.

I notice the plunger isn't hitting the ball dead center on mine but haven't tried to adjust it yet. Mine originally hit the "W" but after adding a little teflon lube it now hits the "A".

For those that want it stronger, I wonder if stretching the spring a little would get the desired results.