Masts and booms are easy, wood dowels or carbon fiber rods or tubes. You can make the mast and boom fittings using a 3D printer or, if you have one, a mini mill using plastic or aluminum.
I might have gotten lucky. I found these just playing around:
Search results for: 'seawind parts' - KYOSHO RC
P01_SEAWINDout
P01_SEAWINDout
P01_SEAWIND KT-431S_out