When we buy a new scope (and this is our first one), we do not have experiences of oscilloscope servicing and replacement parts.
They are two reasons, which someone will start looking for rotary encoder replacement.
1) An accident and a crash.
2) When the scope this passing it second decade of life, at the hands of an expert user.
Today I have become aware of RIGOL company policy, due a YouTube video.
This customer reported, that RIGOL this is willing to sale a new PCB with all encoders onboard for 60$ USD.
And this is the solution for DS1000 series.
The other path, this is of you, shopping alone for replacements.
In this path, you will have to engage with the large and known sellers (chains) of electronic parts.
Possibly you will aim for ALPS (Japan) parts..
Now if you think ordering entire number of rotary encoders = Fail safe thinking = For as NEW working oscilloscope, then the cost of parts and shipping this will not be that economical.
Additionally the responsibility, for performing a proper repair with maximum caution this falls on you.
Here is my personal advice, if your age this is bellow 28 Years old, you better accept the offering of RIGOL.
When this is available due your local authorized distributor.
An rotary encoder this is a very sensitive component, this it should operates with high precision, and also this has a specific service life.
In conclusion, be very careful with your choices.