I have tried looking for the past 4 months for a particular Roku remote for my Roku 3 I tried looking for a replacement controllers tried putting keywords in the description to no avail. So I'm Taking My Chances here.
The type of controller I'm looking for is a controller with the headphone jack since the oh so easy to use private listening app doesn't work on this model as well as a quick button for YouTube
The direct channel buttons were contracted for by the linked-to channels that were included on the remote. There is no way to reprogram them. Different combinations of channels were contracted for at different times, and in units manufactured for different retailers, like Walmart. I don't know if YouTube was ever on one of the buttons.
If you want a new remote with the earphone jack, I think the only one currently available is the "Gaming remote" -- at least its description includes "private listening on your remote" and it does appear to have volume control buttons on the side. Roku accessories page: https://www.roku.com/products/accessories/player
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T