Your question is a bit unspecific since it strongly depends on the available die size, technology and metal stack. There is no typical IC since all of them are very purpose specific. You should also ask yourself how many pins you will need since that is also important factor in how small the die can be. Keeping that in mind 20+ comparators probably don't pose any problems.
Compare possible technologies and do the following for all of them:
- What supply voltages will be used ? -> affects the possible technologies
- Which metal stack to use? (how many metal layers for routing)
- Try to do an area estimate of your comparator
- Figure out how many pins the chip will require and what package you will use
- Do an area estimate of the padring and see if the area fits into the package and the comparators into the padring
- Analog only or mixed signal?
- How much can it cost?
(this list is not complete!)
It is not a simple process in finding the correct answer to your question and without knowing all the specification that you require it is next to impossible.
Good luck!