You will find a great selection of pairs and sets of lights on the Decorative Collecitve from all periods and in all shapes and sizes. Pairs of most things are often more desirable then singles and lighting is no exception.
A pair of table lamps can be situated either end of a sofa for example, or a pair of wall lights can provide better light on a wall rather then just a single. With floor lamps you could actually have a near pair, but make them look more matching by using the same shade on each. Pairs of antiques chandeliers are harder to find, but 20th and 21st Century ones are more readily available. Expect to pay more for a pair purely because of their desirability.