I don't know whether you're still looking or this couple?
I found their three children's births in the British Vital Records so presumably, if this is the correct couple, their date of marriage was a wee bit earlier than you had thought.
Here's the details:
MUIR, Francis Gender: Birth Date: 8 Mar 1817 Christening Date: 19 Apr 1817 Recorded in: Eaglesham, Renfrewshire, Scotland Father: John MUIR Mother: Mary STRUTHERS Source: FHL Film 1041088 Dates: 1816 – 1819
MUIR, Robert Gender: Birth Date: 3 Apr 1821 Christening Date: 15 Apr 1821 Recorded in: Eaglesham, Renfrewshire, Scotland Father: John MUIR Mother: Mary STRUTHERS Source: FHL Film 1041089 Dates: 1821 – 1824
MUIR, Peter Gender: Birth Date: 15 Oct 1830 Birthplace: Abbey (Paisley), Renfrew, Scotland Recorded in: Eaglesham, Renfrewshire, Scotland Father: John MUIR Mother: Mary STRUTHERS Source: FHL Film 1041089 Dates: 1826 - 1841
If the above John Muir was born and lived in Eaglesham, this might be his birth (and that of his siblings)
MUIR, John Gender: Male Birth Date: 20 Jun 1794 Christening Date: 22 Jun 1794 Recorded in: Eaglesham, Renfrewshire, Scotland Father: Allan MUIR Mother: Philips_ LOW Source: FHL Film 1041088 Dates: 1724 – 1800
MUIR, Margaret Gender: Female Birth Date: 4 Mar 1796 Christening Date: 3 Apr 1796 Recorded in: Eaglesham, Renfrewshire, Scotland Father: Allan MUIR Mother: Filips_ LOW Source: FHL Film 1041088 Dates: 1724 – 1800
MUIR, Margaret Gender: Female Birth Date: 19 Mar 1806 Christening Date: 23 Mar 1806 Recorded in: Eaglesham, Renfrewshire, Scotland Father: Allan MUIR Mother: Philips_ LOW Source: FHL Film 1041088 Dates: 1803 - 1806