For sale, my used 3-stalk switch unit for the steering column. Part number 996.613.215.00. Perfect for your OBC retrofit. This is fully working, off of my MY99 with 170000km. I'm about to mount cruise control so have purchased a 4-stalk unit.
Price $50 OBO
Shipping from Poland, so insured shipping is kind of expensive. Within the EU $20, US is $35.
PM if interested.
Edit: added part number