Gardeners, landscaped specialist and nurserymen frequently engage in time consuming searches for choice and uncommon plants to buy. Often the hunt is frustrating, and less satisfactory plants must be substituted for ones originally desired. To help ease the search, Brooklyn Botanic Garden has prepared a guide listing 1,200 trees and shrubs, including shade, flowering and evergreen trees and flowering and low-growing shrubs, with names and addresses of retail and wholesale nurseries throughout the U.S. where they can be purchased.

This new handbook is the Botanic Garden's response to letters and calls from members and friends seeking certain plants, says editor Frederick McGourty Jr.

"It is strictly a public service issue not one of the nurseries cited was asked to pay for the inclusion and the Botanic Garden does not endorse any particular firm. The handbook is simply an attempt to get gardener and nurseryman together concerning 1,200 trees and shrubs, some of them being rare jewels in danger of disappearance from the trade."

The handbook, "Nursery Source Guide," can be ordered for $1.75 from Brooklyn Botanic Garden, 1000 Washington Ave., Brooklyn, N.Y. 11225.

Should specimen-size (rather large) trees the desired, they are usually best purchased locally, especially if they are balled and burlapped, for the cost and danger of shipping large plants is substantial, the handbook points out.

Some regional firms that specialize in uncommon species of landscape size are listed in the handbook, but enthusiasts may have to drive long distances if the nursery does not have a truck delivery service in their area.

A local nursery may often try to assist you in obtaining larger sizes of uncommon trees. You can assist by providing the wholesale source of particular plants provided in the handbook.

Many fine shrubs and trees are unavailable locally, but there are mail-order firms that will supply these plants, generally in modest sizes. With the exception of evergreens and a few other plants that nurseries usually ship in pots or with small balls of soil, woody plants are sent bare-root, with plastic wrapping and sphagnum or similar material to keep the roots from drying out.

Since bare-root plants may be sent only when dormant, the common shipping seasons, depending on climate, are October to December and March to May.