You need to use ScotlandsPeople to find his birth registration.
https://www.scotlandspeople.gov.uk/?...FRMRtAodETkA_g
Hopefully this will give you his mother's maiden surname.
If you can find him in 1901 and he is with his parents then you should have enough info to find his parents marriage. In general, Scottish BMD records have more information than those from Eng/Wales. To download the info, you need to buy credits for the site and then use those credits to get the certificates etc that you need.