Is there such a thing as an enameled cast iron sink with a large single bowl (at least 25") plus a drainboard? If I could design my perfect sink that would be it.
The Sandford sink is a reproduction of the old-fashioned cast iron drainboard sinks. The total width is 42", but the sink well is less than 25" wide.
I saw a fireclay one that looks really nice and is the right size, but I wasn't sure about the fireclay material and it's durability. I have had great experiance with my current Kohler enameled cast iron sink, so I was trying to stick with that material.
This sideboard kitchen cast iron sink from DEA Bath has a basin that's 17 by 24 inches, so not quite 25 inches which is what you said you were looking for, but it may be close enough for you. It's the one at the top of the page when you follow the link below.
Here is a link that might be useful: sink