The Medal Index Card should give details of his medals and the date he went on active service. It should also give the date active service commenced. These are abbreviated and not always easy to decipher.
Depending on when he was sent on active service he should have been entitled to:
EITHER 14 Star - the 1914 Star (the "Mons Star" issued to regulars and volunteers on active service in 1914)
OR 15 Star - the 1914-15 Star (issued to regulars and volunteers on active service in 1915 - before conscription began in 1916)
AND BWM - the British War Medal
AND VM - the Victory Medal
Philip
ADDED - it is not possible to buy official duplicates of Great War medals, but replicas are readily available on sites such as e-bay. The original medals were engraved with name, number, and unit - these come up on e-bay but I wouldn't feel comfortable buying a named serviceman's medals and attributing them to my relative.