I have a George Murison born 1804 who was the son of George Murison and Elizabeth Murison but do not think they ever married, does anyone have any info- George junior, died in 1873 and he was married to Susan Burnett, he was gt.gt. grandfather
I assume that you have George Jr's death certificate, that you got his parents' names from that, and that his mother's name is shown as 'Elizabeth Murison' not as 'Elizabeth Murison m s Murison'?
If so, then you are right, George and Elizabeth were not married to one another.
I note that the SP index says that he was aged 69 when he died in 1873, and that his was the third death registered in 1873. Therefore he must have died in the first few days of 1873. He would almost certainly not have had his 1873 birthday, when he would have turned 70. So it is far more likely that he was born in 1803 than in 1804, assuming of course that whoever registered the death got his age right. And there isn't a record of a baptism that could fit, unless it's the one with father George Murison, no mother named, in Fyvie in 1808.
All the censuses (transcriptions at
https://www.freecen.org.uk/cgi/search.pl) say he was born in Fraserburgh. The best chance of finding out anything about his parents is to try the Fraserburgh Kirk Session records. If either George Sr or Elizabeth was a member of the Church of Scotland, the KS would have got wind of her unmarried pregnancy and would have summoned her to be disciplined. This involved telling them who the father was, and summoning him to be disciplined with her. The KS records can sometimes be quite revealing.
The surviving KS records are in the National Records of Scotland, the volume you want being catalogue reference CH2/1142/7. These records have been digitised, but are not (yet) available on Scotland's People. You either have to go, or get someone to go on your behalf, to the Historical Search Room in Edinburgh, or to one of the local archives that has access to them (Aberdeen, Hawick, Inverness and Glasgow that I know of, and there may be others).