Ogham was a Dublin-based folk label, distributed by CBS Ireland.
Ogham seems to have been related to Blackbird Records, though I'm not exactly sure what the relationship was - shared management? The two labels certainly appear to have shared catalogue numbers. The Makem & Clancy releases below are Blackbirds; the De Danann and Clannad releases are Oghams. Maura O'Connell releases are shared between the two.
Blackbird & Ogham Singles All 7" singles unless otherwise indicated. Prefix BB.
Ogham Albums BLB 5001 Clannad – In Concert  BLB 5002 BLB 5003 BLB 5004 Seán Cannon – Erin The Green (Songs from the Irish Tradition Sung By)  BLB 5005 Seán Keane – Fiddle and Viola  BLB 5006 De Danann – The Star Spangled Molly  BLB 5007 Maura O'Connell - s/t (1st)  BLB 5008 Derek Bell (Chieftains) - From Singing to Swing (Tausig, Field, Paderewski, Grieg, Scott, etc)  BLB 500? Clannad – Crann Ull (1981) [quickly replaced by Tara pressing] Blackbird Albums BLB 1001 Makem & Clancy - s/t  BLB 1002 Makem & Clancy - Concert  BLB 1003 BLB 1004 BLB 1005 BLB 1006 BLB 1007 Makem & Clancy - Two for the Early Dew  BLB 1008 Liam Clancy - The Dutchman LP  BLB 1009 Makem & Clancy - Collection LP  BLB 5009 The Clancy Brothers and Tommy Makem – Reunion 
Blackbird BB 101 Makem & Clancy - The Band Played Waltzing Matilda/Town Of Rostrevor & Maggie Pickens  Blackbird BB 102 Rubbish - Hey C'mere / A Tribute To the Chairman  B-side confirmed Blackbird BB 103 Makem & Clancy - The Town of Ballybay / Kitty From Baltimore [1977?] Blackbird BB 104 Makem & Clancy - The Dutchman / The Lowland Sea [1978?] Ogham BB 105 Clannad - Down By The Sally Gardens / An Giobog  Blackbird BB 106 Makem & Clancy - Red Is The Rose / Bower Madden  Blackbird BB 107 Makem & Clancy - Morning Glory / Cruiscin Lan  Blackbird BB 108 Makem & Clancy - The Garden Song / Tombstones  BB 109 BB 110 Blackbird BB 111 Makem & Clancy - A Place In The Choir / Sliabh Gheal Gua Na Feile  Blackbird BB 112 Makem & Clancy - Ballad of St. Anne's Reel / Sliabh Galleon Braes [1980?] BB 113 Blackbird BB 114 Makem & Clancy - Waltzing Matilda / Red is the Rose (PS)  Ogham BB 115 De Danann - Maggie / The Cuckoo's Next Medley (PS)  Blackbird BB 116 Makem & Clancy - Rainbow Race / Dear Dark Eyes  Ogham BB 117 De Danann - The Star Spangled Molly / Boys of Malin  BB 118 Ogham BB 119 Maura O'Connell - Saw You Running / It's A Sin To Tell A Lie [1981?] (PS) Blackbird BB 120 Makem & Clancy - Whatever You Say, Say Nothing / Gentle Annie  Blackbird BB 121 Maura O'Connell - Til The Right One Comes Along / Sitting On A Runway  produced by P.J.Curtis in Nashville Ogham BB 122 Maura O'Connell - Like In The Movies / Where I Belong To You  (PS) BB 123 BB 124 Ogham BB 125 Maura O'Connell - Feet Of A Dancer / Always  Ogham BB 126 Maura O'Connell - If You Love Me / Just A Song At Twilight  Produced by Bela Fleck at Nashville Sound Blackbird BB 127 Makem & Clancy - The Tale Of Bridie Murphy And The Kamikaize Pilot / The Newry Highwayman  Blackbird BB 128 Makem & Clancy - We Are the Boat / Dandelion Wine [1986?] Ogham BB 129 Maura O'Connell - Another Morning / The Harvest Song  (PS) BB 130