DB Electrical, they sell them via eBay. Decided getting a new one would be better long term than a rebuilt. No issues so far. Upgraded to a 90amp turbo version for my NA.
One trick when installing the new alty, use some duct tape to hold the rear nut in place. Makes it so much easier trying to get the alty and bolt all lined up without also trying to keep the nut in place. Have used this trick twice.