It is unusual for a controller to need an analogue input, are you sure this is what it needs and not a PWM input?The answer to this question decides which of two solutions you need.
Post the datasheet/product page for the dimmer in question please...
You will have to look for an external DAC. This one may not be too useful (just one DAC), but there will be with more outputs available.As it's I2C you can add as many DACs on just two pins as they have unique addresses available. You'll be addressing them digitally (by writing a value to a register), and get an analog voltage out.
I found this huge list of DAC's, but dont know if they are that what I need
Is it important which bit version i order. (12 or 16)Also: Do you have a photo of a thing like this. How big is it? Maybe an guide how you use these things?Edit: Also there are different version in the shopping window.. whats the difference:
You need 20 lines then how about 2 of the 12's?