I am not aware of one single amplifier manufacturer that designs a matching passive preamp to compliment their amplifiers.
Three manufacturers were mentioned in this thread: Roger Modjeski - Music Reference, Jack Elliano - Electra Print, and Jeffrey Jackson - Experience Music.
Also, a number of manufacturers have implemented passive volume controls in their integrated amp designs. A couple that come to mind are Vinnie Rossi - Red Wine Audio and Paul Weitzel - Tube Research Labs. Ralph Karsten at Atma-Sphere offers a passive volume control upgrade for his OTL designs too.