Searching replacement for CM8870
The HT9170 is a compatible replacement for the CM8870. They are both DTMF Receivers. They are pin compatible (18 pins) and the HT9170 has a wider operating voltage (2.5 to 5.5V), while the CM8870 works with 5V supply.

The MC145436 is also a DTMF Receiver, but is not pin compatible with CM8870 or HT9170. The MC145436 has 14 pins instead of 18 of the other two.

Here are links to their datasheets: HT9170, CM8870, MC145436