I don't know the author either, but will definitely do further research for you.
Update 6/11/09. Still no positive word Narisha, I went as far as to check with the National Library of Jamaica (NLJ) and they admitted they don't have a record of the author either, although they are aware of the song.
Jamaica National Heroes Song:
Forward, Forever United Which We Seek You Seek
Chorus: Forward, forever united Students workers and farmers
1. Granny Nanny of Nanny Town symbol of unity and strength lighted the flame of freedom in the hearts of earlier Jamaicans
2. Sam Sharpe, non-violent leader instigated the slaves of Jamaica to fight for freedom and liberty and throw off the shackles of slavery
3. George William Gordon, far seeing statesman struggled for human rights and dignity he was unjustly executed for raising his voice against oppression
4. Paul Bogle of Stony Gut fought against oppression and deception leader, preacher and martyr he died in the cause of justice
5. Marcus Mosiah Garvey fighter of Black Man's dignity throughout every nation he gave all black man a dream
6. Patriot Norman Manley made politics an instrument of progress father of the nation man of integrity and justice
7. Alexander Bustamante a ledgendary figure in his lifetime indomitable labour leader first Prime Minister of Jamaica
Final chorus Forward forever united Jamaica united forever