What you could do is: take a 4017, clock it to 4 outputs high, so feed the 5th output back to reset, connect the 4 outputs to a PAL(16V8?) and to the colomns of the keyboard. Put the 4 rows to 4 other inputs of the PAL and have 1 output of the PAL generate an interrupt.
If you take a PAL22V10 you could make the outputs latching. The outputs of the PAL contain the data.