The same trouble happened to me. some times it is hard to get chips for one or other reference. nevertheless, I solved my problem making an adapter which converts PLCC to Dip(P89c51xx I got) and my board works fantastic.

Do not be afraid, it is compatible pin by pin. Perhaps, it is silly to recommend you pay attention the first time you enter the ISP of the chip and want to enable the default bootloader for the future, you have to change the Status byte and put back the value of BootVector, otherwise you loose the chip.