The person I am chasing is Marion born 1823. I can't locate a birth certificate for her.
There isn't one to find, as birth certificates did not exist before the start of civil registration in 1855.
The best you could hope for would be a baptism, but there are many gaps in the registers of baptisms.
There is a death certificate, however; Marion Pennycook, mother's maiden surname Porteous, died in Inveresk and Musselburgh in 1886 aged 63.
The 1851 census lists a Marion Pennycook, aged 28, cook, born Lasswade, in the household of Thomas Constable in Duddingston.
Both these records put her birth in either 1822 or 1823, assuming they are accurate. And, of course, that they are one and the same person.
Helen Pennycook, other name Porteous, mother's surname Brunton, died in Cockpen in 1867, aged 75. Her death certificate might be worth a look.