This type of compulsive behavior is not common after a stroke. Although I don't know the details of his full treatment, I am a bit suspicious that one of his
physicians started him on a "dopamine agonist" medication for his Parkinson's symptoms. I would check this with the Movement Disorder specialist. These medicines cause, what I call, a "Las Vegas" syndrome - whereby people partake in risky, compulsive behavior, such as hypersexuality, gambling, risk taking, spending, etc. If he is on one of those medicines, I would try to get him off it and on to an alternative such as Sinemet. Please talk to your doctor about that.
If he is not taking one of those medicines, I would recommend seeing a Psychiatrist and possibly starting on a low dose anti-psychotic medication to help take the edge off these compulsive behaviors.