Daniel,

The first thing one needs to know about Scottish coats of arms is that they are not "family" arms, but are granted to individuals.

That being said, "An Ordinary of Arms," vol. 2 ( collection of all coats of arms granted by the Lord Lyon King of Arms; vol 1 1672-1901, and vol 2 1902-1973 ) contains an entry for Maj. Alastair Joseph Edgar Cranstoun of that Ilk and Corehouse, granted 11 September, 1950:
"Gules: three cranes passant Argent." That means three silver cranes walking to the viewers left, on a red shield. His motto is: Thou Shalt Want Ere I Want. He bears as a crest "a Crane Proper dormant holding a stone in her claw."

In addition, the achievement also contains a grant of supporters:
"Dexter, a lady of the 16th century Proper, richly attired Vert, slashed and ribboned Gules, holding in her exterior hand a bunch of strawberries Proper; sinister, a buck Proper, armed and unguled Or."

Three other Cranstouns bear arms, which are based upon the Cranstoun of that Ilk arms with the addition of differencing borders.