Of course, it depends on the scale, but Scale Shipyard makes 1/48 and 1/96 destroyers and fittings (more in 1/96 scale) (www.scaleshipyard.com)
John Haynes makes some nice 1/96 scale DD parts too. (johnrhaynes.com)
Don Preul makes a few Cold War Era DD (www.jdprod.com)
Loyalhanna Dockyard carries many lines of 1/96 scale items (www.loyalhanadockyard.com)
There are quite a few others, depending on the size and nationality of the vessel in question. For a more comprehensive list of links, see my links page:
http://wmunderway.8m.com/links/links.htm
Be sure to check out the main site as well, Warship Models Underway, as it is devoted to large scale warship modeling:
http://www.warshipmodelsunderway.com
Cordially,
Kurt