Like the economy generally most marine trade service providers have fragmented into self employed contractors with the marina owner often the landlord. many clubs have abandoned the slipways due to the cost of works to comply with environmental requirements.
I note Ryan Short Marine that operates at Fergusons Boatshed Marina at the Spit advertises all the services (including electrical) that you mention. Here is the link to their website
boatdeck.com.au/wp-signup.php?new=ryanshortI use Michael Bartley at Woolwich Marina (not Woolwich Dock) who has does excellent work. Give Michael a call and discuss your needs. His number is 98794222