do you know the school and county from which you received your GCSE?
You need to contact the school for a copy of the record from archive. Now the problem is, that they may not keep the records for longer than 10 years.
Start out by contacting the school: http://www.johnmasonschool.org.uk/
Then if that does not work contact the agency responsible for the testing:
Textphone:(NNN) NNN-NNNN6546Fax:(NNN) NNN-NNNN6666 Email: email@example.com
You can also access this site and request a copy of results...there is a fee.
( http://www.aqa.org.uk/admin/library/AQA-examrecords.pdf ).