In one option you can build a generator around 2 gates (2 x 1/4 7400) with 2 resistors and 1 capacitor to set the desire frequency and use the 2 remaining gates as buffers,
or
you can build a generator around 555 working as astabile and use 1 digital transistor with a pull-up resistor to invert the output,
or,
,...... many other options ..
Added after 3 minutes:
1 x 74HC/LS123: 2 monostanile connected in a closed loop ..