Used to could buy.

source: 
LAGS
Entry: 
639
Example: 
Used to could buy.
Modal 1: 
used to
Modal 2: 
could
Gender: 
Male
Race/Ethnicity: 
White
Age: 
79
Level of Education: 
6th grade and self-educated
Home Community, Town, or State: 
TX (Schulenburg)
Location Collected: 
TX (Schulenberg)
Year: 
1978
Relation to Addressee: 
subject to fieldworker
Medium: 
Spoken
Sentence Structure: 
1.0
Status: 
Naturalistic