replcement of MC34063a

hello everybody,
iam wondering if somebody know any replacement of IC
MC34063a
cuz this IC r not availble in my Local area

You need for negative supply or as step-down converter?

i don't know
cuz i got the circuit design of eprom programer
i almost finshid building pcb but i couldn't find this ic
i think i did mistak by building pcb without being sure of all component r
on stock
:cry: :cry: :? :?

If you need the chip to make a voltage convertor for a programmer, why not use a 78S40 instead, as this is available. OR raise the supply volts to the programmer and then use an adjustable reg like the LM317 to obtain the desired volts for the pgm voltage......?