I haven't seen any HDK parts or accessories on any of the golf cart parts suppliers websites. The only places I've been able to find parts and accessories for them is on the HDK website and some stuff on ebay and Amazon. Maybe some others members will be able to help you out.
Welcome to the forum.
Do you think pulling this rear axle out and swapping it with another brand might work? What would be some of the challenges?
I had a Jeep an swapped rear end for a Ford Rear end ... just for reference ...