Antiques and old stuff are found all over Turkey—this is a very old country, after all—but the best antique shops are undoubtedly in Istanbul.
Perhaps because they were the first, or perhaps because Istanbul has a larger number of people who appreciate antiques, this city is the center of the trade.
For help in finding exactly what you're looking for, call on Marilyn Hill-Henderson.
Check out the Grand Bazaar's central Old Bazaarsection, which has been the place to find odd and curious treasures for about a thousand years.
The shops here specialize in old prints, paintings, maps, home decorations, furniture, glassware, old weapons, etc.