I would advise looking for Maria and David on all Scottish censuses.
You say you have them in 1851, but what about later censuses? You might be lucky that their birth place is noted in more detail than just "Ireland".
You are unlucky in that the 1871 census was taken on the night of the 2nd of April and David died on the 1st, but you should be able to find him in 1861.
It is likely that Maria and David came from a similar area, so even if you find Maria in 1871/81 after David's death, her pob might give you something to go on.
That is unlucky. This is what I have for David:
1841
Name David CrosgroveAge 40
Estimated Birth Year abt 1801
Gender Male
Where born Ireland
Civil parish Girvan
County Ayrshire
Address Chapedonan
Occupation Cotton H L W
Parish Number 594
Household Members
Name Age
David Crosgrove 40
Maria Crosgrove 30
James Crosgrove 14
Mary Crosgrove 12
Elizabeth Crosgrove 10
Jane Crosgrove 8
Henry Crosgrove 5
Margaret Crosgrove 2
1851
Name David CrossgroveAge 53
Estimated Birth Year abt 1798
Relationship Head
Spouse Moriah Crossgrove
Gender Male
Where born Ireland
Parish Number 600
Civil parish Kirkmichael
Phillimore Ecclesiastical Parish Maps 9089
Town Crophill
County Ayrshire
Address Dalhowan Back Road
Occupation Weaver
ED 8
Page 30
Household schedule number 107
Line 14
Roll CSSCT1851_134
Household Members
Name Age
David Crossgrove 53
Moriah Crossgrove 47
Mary Crossgrove 22
Elisabeth Crossgrove 20
Jane Crossgrove 18
Henry Crossgrove 15
Margaret Crossgrove 12
David Crossgrove 9
Thomas Crossgrove 5
1861
Name David CrossgroveAge 63
Estimated Birth Year abt 1798
Relationship Head
Spouse's Name Mariah Crossgrove
Gender Male
Where born Ireland
Registration Number 600
Registration district Kirkmichael
Civil parish Kirkmichael
County Ayrshire
Address Back St E Side
Occupation Cotton Weaver
ED 8
Household schedule number 112
Line 17
Roll CSSCT1861_87
Household Members
Name Age
David Crossgrove 63
Mariah Crossgrove 55
Jean Crossgrove 26
Margaret Crossgrove 24
David Crossgrove 19
Thomas Crossgrove 14