Finding a door knob or light fixture is no easy task if you own an old house.

You can go to the neighborhood allpurpose hardware store chain but what you will find belongs on the hardware store's version of a suburban ranch house. Unless you have one or want your fine old house to look like one, they are of little help. If you own an 18th century house or a Williamsburg copy, you can find an appropriate substitute through a few hardware stores and interior decorators. But if you own a late 19th century rowhouse, a country farmhouse, or a Queen Anne mansion, you will have to become a scavenger and a clever one. The convenient sources just won't have what you need if you want to retain the character of the house.

Owners of old houses often turn to cannibalism in their search for a parquet floor or heating grate. They get to an old house shortly before it is to be torn down and buy the part they need from the foreman of the wrecking crew in a "cash-only" deal. They spend their weekends at salvage yards, antique sales, and junk shops. If they are lucky, a neighbor will have a spare of whatever they need and be willing to trade or sell.

The city of Baltimore has institutionalized this process with a salvage depot that sells parts of old houses. You have to be a Baltimore resident and promise to use the door, mantle, or bathtub in a Baltimore house. Other cities are thinking about copying the Baltimore idea.

The boom in housing rehabilitation is beginning to change the situtation for owners of old houses. It is possible, with a lot less effort than before, to get the piece of hardware you need and sometimes from the roiginal manufacturer. In other cases, new companies are being formed to make the old product. A demand for pressed metal ceilings brought a former manufacturer into the business again, and a new company has been formed to make, in fiber glass, the ornamental iron cresting that decorated the rooflines of 19th century buildings. There is still the problem of distribution.

Because of the relatively small demand (thousands are not clamoring for the cresting), the hardware store chains and building materials suppliers just won't stock many of the things the owner of an old house would want to buy.

Beverly Reece is associated with the Preservation Resource Group.