Switching 100 different LM35 with one uC
If you are using LM35 for the +2°C to +150°C range which outputs positive voltage only then an analog switch like 74HC4066 or 74HC4016 seems fine.
The Maximum ON resistance of the switch is the range of 100 to 200 Ohm which would work fine with the ADC input of the AVR.

If you intent to use the full range −55°C to +150°C then the negative voltage will be a problem with the switch.

Since you intend to use 100 switches in groups of 8 you can bridge the control inputs together for each group, then you can lower the control pins needed to 100/8 = 13 pins
To reduce that even further you can add a couple of shift register like 74HC595 and use the outputs to drive the control inputs of the analog switches.



Is the use or the analog sensors a requirement?
If not I would suggest the use of a digital sensor like DS18B20 that will give a higher accuracy and easier deployment using just a few wires without the need for switches.