Yikes! I got mine from SeaDoo Parts House. But also... no longer in stock!
When this happens, I call my friendly parts guy Gannon at Sky Powersports in Cocoa Florida, (mostly motorcycles- and not even a certified Sea Doo service center, yet). He searches all the other shops in Florida to find one and he usually does. I prepay over the phone, and they ship it to him for me to pick up.
So, google and call your local Texas Sea Doo service/parts shops like a motorcycle shop if not a boat shop and ask them to search shops for you state or even nationwide if needed. You need a FRIENDLY parts guy though.
It is still STEERING CABLE 204390587 by the way.
It sucks, Sea Doo abandoning their customers. I've had terrible challenges myself. If my new throttle handle breaks off again, no longer available...I'm screwed!
The frikken SeaDoo manual itself causes us to damage our boats. It says spray that SeaDoo X crap whatever lube on everything. Well, it degrades and cracks rubber and plastic by leaching out all the oils and makes it brittle.
It caused my rubber seat and ladder straps to break off, the rubber boots on both my steering and reverse cables swelled and fell off, causing premature cable failures from saltwater intrusion ($1000+ labor), and causes dried gunk in the cable to make your gear lever hard to move. Finally my throttle gear lever broke completely off because I was using their recommended spray on it and it caused it to crack! $700 + labor, also no longer available!
By the way I'm using small stainless hose clamps to secure the black rubber bushings on the steering and reverse cables this time. Suggest you do this too. So they don't swell and fall off like mine, if some service center sprays lube directly on them like I did, they will swell.
Sorry for writing a novel. This is kind of helps me too. Please let me know if you do find your steering cable with contact info... I'll be needing one down the road again as they rust out every 10 years!
Good luck!