When I can?t find something locally I just go to amazon. They have EVERYTHING!! Lol
HelmsMate Tiller Extension Handle. Five models ranging from an 18" fixed length model to an extendable 37" to 51" length model with a Universal Joint. (18" - 24", Adjustable)
https://www.amazon.com/dp/B00MYSZQZU..._qRZbBbK245N35
Just do a search on amazon there are lots of choices.