Hi Peter,

Instead of 3 x 4066 have you thought of using TWO x 4051 "back to back" instead. 4051s are common enough and cheap enough to be around for a long time yet

Provided the combined series resistance of two crosspoints is low enough to drive the keypad you can use that to address a keypad of upto 8 x 8.

To drive the 4066's you will need quite a few I/O lines or some form of IO expander whereas with the 4051 method you only need 6 lines for a 64 key 8x8 matrix and in your case get away with only 4 IO lines.

Mux "a" on the rows using a & b address lines with line c tied to 0v
Mux "b" on the columns using a & b address lines with line c tied to 0v

connect the "common" terminal of each mux together.

4051 is also available as an SMDso you can fit a pair of them in the same space that a normal DIP would take if you need to.