I used to could play a harp.

source: 
LAGS
Entry: 
687
Example: 
I used to could play a harp.
Modal 1: 
used to
Modal 2: 
could
Gender: 
Male
Race/Ethnicity: 
White
Age: 
77
Level of Education: 
10th grade
Home Community, Town, or State: 
MS (Homewood)
Location Collected: 
MS (Trenton)
Year: 
1974
Relation to Addressee: 
subject to fieldworker
Medium: 
Spoken
Sentence Structure: 
1.0
Status: 
Naturalistic