You could check what Zodiac make (Bombard is part of that group), or get one made.
The stuff on Ebay will be poor quality in my opinion. You want 316 stainless up to 2" diameter tubing, and think about how it's actually going to attach to the boat. If it's bolted to the deck, then you need to think about access (possibly cutting access holes). These things can't be secured with self-tappers. Maybe an option to have the main supports on the transom where bolt-through is easier. Post up some images and layout.
Also think about tow point if you wanted it for water-skiing, navigation lights and VHF antenna base.
I used these guys for a bespoke collapsible light-pole.
https://marinefabrications.co.uk/
Some nice work here too. (I've no knowledge of this business - but the gallery images look excellent.)
https://www.mrstainless.co.uk/portfo...tegory/marine/