In the 74922 datasheet pag 8 there are an example of 32 key decode.

If you need the same may be you can do the same with the 933 for 2x20=40 Keys

If not, you can do a matrix of 6x6 = 36
6 lines (port pins) are outs and 6 are in. Then sending zeros by outs you can read the ins if some key is pressed.

Regards.