This locomotive has a mushroom type smokestack that fits over a smaller cylindrical stack. I lost the mushroom smokestack and would like to replace it.
Bachmann makes a 4-4-0 with a spark arrestor stack that used to slip over the straight stack. So you may want to check Bachmann parts.
This thread piqued my interest. I've been in N Scale for 50+ years and wasn't even aware of this locomotive until I looked it up. It appears in my 1985 Walthers catalog under Model Power's section (they bought Minitrix) under three stock numbers -- 2080 (UP), 2081 (PRR) and 2087 (AT&SF). Spookshow reports that it was introduced in the late '70s. These seem to have had a much shorter run than Minitrix' PRR-based 0-6-0 that was produced for a long time.
I checked Atlas and alas no parts as far as stacks currently and while I was at it Bmanns stock is not showing the stack. Looks like Shapeways may be the only option. Even checked my parts box. This particular loco is running on my pike as a tank engine now.
