Source for older model 4-6-2 pacific steam engine

I believe there are, unfortunately most of them are two rail brass locomotives.

Might be able to 'bash one from an old AHM 4-6-0, which has the right firebox.  I have seen examples of it made into Pacifics.

What Palallin said.  With those turn-of-the-century high domes, I would start with a 4-6-0 or even a 2-8-0.  Detail and decal it for the GN, to look like the loco in the picture.  As to the wheel arrangement, a chassis transplant will take more than just a Dremel tool and some bondo.  So I would squint hard and use your imagination!

There are brass boilers and partial brass locomotives that appear on eBay. I've bought a couple. Combining one of these - that is, one that at least approximates the basic shape you need, and, if you are lucky, some basic features, like a Belpaire firebox - with a chassis will probably be your best bet. Depending on the basic dimensions you need, even a 3RO traditional- or RK-sized 4-6-2 might do. The prototype appears to be a smaller loco, and the RK (etc.) loco would probably be cheaper than a full-scale loco.  Discard the factory superstructure and adapt the brass. The tender is a box tender, and could be plausibly adapted from a production piece.

Stephenson Preservation has detail parts.

Perhaps a PRR K-4 Pacific (Traditional? 1:48?) could be used in its entirety - it has a Belpaire firebox, but needs all sorts of changes otherwise, of course, (The detailing is the fun part, though.)

Compromise is important.

AHM are 2 rail, so would boiler even come close to fitting  on k line semi-scale pacific  chassis.  Also looking at Sunset Hard Iron K-4, any thoughts? DON

The 3rd Rail High Iron K4 is a little large for the GN locomotive you are looking to replicate.  Also, GN's design of the Belpaire fire box is a bit different than the PRRs.  GN's appear to be a little boxier than the PRR versions.  It looks like the drivers are somewhere perhaps in the 65" range?  Just a guess.  As other posters have mentioned, an older AHM body with modifications and detailing mounted to a traditional sized chassis for the motor and main drivers might be the best route.  You can always change the pony trucks out.  Cool that this little Pacific had a booster engine on it.  Definitely worth capturing in one way or another. 

Another route that has been suggested might be to search for an older 2 rail brass donor as a starting point. 

However you figure it out, that is a nice small Pacific that would be great for smaller scale layouts. 

Thanks for all the help! I am going to find and modify a k line  k4. The AHM is just way too small to haul 5 -7 Labelle passenger car--I would rather be too big then too small. Thanks again. DON

I know you've made your choice, but it just dawned on me when I looked up at the currently month in one of my PRR calendars in the office that the PRR G5 might make for a closer model with less work.  You could put that trailing booster truck under the rear of the cab. 

Random thought.