I used to could.

source: 
LAGS
Entry: 
641
Example: 
I used to could.
Modal 1: 
used to
Modal 2: 
could
Gender: 
Female
Race/Ethnicity: 
White
Age: 
71
Level of Education: 
10th grade
Home Community, Town, or State: 
FL (Rockmart)
Location Collected: 
FL (Rockmart)
Year: 
1973
Relation to Addressee: 
subject to fieldworker
Medium: 
Spoken
Sentence Structure: 
1.0
Status: 
Naturalistic