Thank you, both of you.
That Atlas bridge is what I was looking for. My "local" hobby shop carries Atlas code 55, but they didn't have any bridges of any kind.
I don't need one exactly like the one I have, but would like to replace a Kato through-truss with a through-girder bridge, and don't need the full length of the truss. Like the Milwaukee Road, overhead wire and through truss bridges can be inconvenient. It's very hard to clean the track in that bridge!