I got the paint that Olsens Toy Trains sells and it was an exact match. Comes in a tin/metal container and I thinned it with paint thinner. I think it's available in a spray can as well.....or at least it was 7 or 8 years ago when I did these...
I repainted all three sets and the paint came from Olsen's for all of them. Maybe the Train Tender (not 100% on that), but pretty sure it was Olsen's.