Unfortunately, Ancestry doesn't have access to Scottish BMD records. You can try https://www.familysearch.org/
which has most of the OPR records, but the best site is http://www.scotlandspeople.gov.uk
which is pay to use.
My ancestors are form Ayrshire. As well as Renfrewshire, they can often be found in Lanarkshire so it's worth widening the net. But ireland is also a possibility - it's a very short distance from the north of Ireland to the Ayrshire coast.