Sorry to be late to the discussion.
As far as I know the original Maine two footers exclusively used chilled tread cast iron wheels- some by Griffon, some by Portland Co.
Edaville's replacement wheels were forged steel- the modern standard. We also have purchased some of these- for our caboose and for one replacement wheel set for coach 3.
5 years ago the price per wheel (not wheel set, one wheel) was about $2100. So any new piece of rolling stock involves around $17,000 just for wheels (probably more today).
We are considering producing wheels "in house" by making a pattern matching the old Po Co wheels, having them cast by steel, gardening, then machining ourselves. We'll have to compare total cost. We'll also have a more historically correct wheel.
Couplers- same story. 3/4 couplers are commercially available- around $2000 each. We've also considered making a pattern for this.
We currently have two new couplers in hiding here at the shop- which we are saving for the coach replica project. Which needs wheels...
See ya
Jason