Might couldn't.

source: 
LAGS
Entry: 
313
Example: 
Might couldn't.
Modal 1: 
might
Modal 2: 
couldn't
Gender: 
Female
Race/Ethnicity: 
White
Age: 
62
Level of Education: 
5th grade
Home Community, Town, or State: 
GA (6 miles from Milledgeville)
Location Collected: 
GA (Milledgeville)
Year: 
1970
Relation to Addressee: 
subject to fieldworker
Medium: 
Spoken
Sentence Structure: 
unknown
Status: 
Naturalistic