Hi,
Quite straight forward:
Since sinusoidal signals are analog signals:
Go to any electronics distributor's internet site of your choice and do a search for "analog MUX".
Hints: you will need to decide your requirements (mainly technical / electrical specifications) first. No one can do this for you.
You are not the first one doing this, thus you will find informations / circuits / solutions in the internet.
Also the ADC vendors and analog_MUX vendors provide application notes. Use them, they are for free.
Klaus