Have you thought about making sprung vertical plungers? They could even be offset from center slightly with end bracket and side thrust angling.
Solder square tube/ rod (keystock) to a Lionel " modular" pass car roller part (just the metal "T" toss the plastic) Plastic/nylon tube/rod if/where it needs to be insolated.
Or a wide button/mushroom head shoe? (360° wobble disc) Ive made these from low profile, wide, carriage bolt type heads and from HUGE brass decrative tacks too.
Shoes have better pickup imo, but have a much higher drag too. Each shoe set's drag equals loss of at least 2 roller cars of pull is my estimate