G.E.,
The DeGolyer has the following blueprints for the Sonoma:
1) Replacement Firebox
And that's the full list. They have quite a few drawings for 8-18-Cs, but they could be for anything from 30" to 60" gauge engines. The Replacement Firebox drawing is the only drawing specifically for the Sonoma (8-18C-25)
There are two source for drawings for the Sonoma, Cal. State RR Museum Library, and me. What they don't have drawings for I ended up creating drawings for in the course of making that side elevation model. Special thanks to Dan for letting me take mearsurments from the Eureka, and to Nv. State RR Museum for letting me also measure some parts of the Glenbrook for comparison and design-intent research.
If you have a DXF file viewer & a ZIP program:
[home.att.net]
However CSRM Library has alot of drawings for the Sonoma from Baldwin & many prints they made themselves for the tender & detail pieces.
Cheers,
Curtis