If you are having trouble finding them, it's probably because you're not looking in the right place yet:)
Neil McArthur and Mary McTaggart were married in Bonhill in 1913.
Their daughter Mary was born in Bonhill, also in 1913.
Go to
www.scotlandspeople.gov.uk and invest in a few credits. Use some of them to download the marriage certificate. It will tell you the couple's ages and the names of their parents, including their mothers' maiden surnames.
Then use that information to look for the births of Neil and Mary, and so on back to 1855.
There is a birth of a Neil McArthur in Bowmore and Kilarrow in 1890, mother's maiden surname McVorran. (McVorran could be a non-Gaelic-speaking registrar's misunderstanding of a Gaelic surname, so if you have trouble finding McVorran try McMorran.)