if you find a ribbon with the same stitch count but not the same yards then it often works to get the same amount of yards (more balls). But if may change the density.
My best bet would be to look at the original yarn closely without buying it and then buying something in a shop that you can actually look at / feel. Maybe they even have both at the same shop and you can compare one to one.
definitley stay with a ribbon though. Same width, if possible (that you can mostly only check out yourself) because that makes a lot of the look of a piece.