Publication not available to carry a declaration of rights (5,5)
I believe the answer is:
magna carta
'declaration of rights' is the definition.
(charter of rights signed in England in 1215)
'publication not available to carry a' is the wordplay.
'publication' becomes 'mag' (abbreviation for magazine).
'not available' becomes 'na' (abbreviation for not available).
'to carry' becomes 'cart' (carting is a kind of carrying).
'mag'+'na'+'cart'+'a'='MAGNA CARTA'
(Other definitions for magna carta that I've seen before include "Old document" , "Document signed by King John" , "1215 charter" , "Document signed twelve fifteen" , "historic document" .)