Charles: Aurangzeb Haque has stated that he is not following a proven design but has made several changes to it. In order to know that it is programing correctly he must know the exact timimg and voltage levels that the target chip is seeing. He can not confirm these without a scope. Further he needs the correct data for the chip he wishes to program. Good luck Aurangzeb Haque you will need it.

As to the availibility of these older chips you probably will be able to get them for some time But from the same sources you can probably get current product as well. A beginner needs one chip to learn on. Later for a small project he might want 50 or 100 - then the cost savings might be justified but I doubt it. If the chips are used well that is just more problems for the beginer to face.
An experienced hobiest can do well with these chips , but a rank beginner will spend much more trying to get something like this working that it can possibly be worth.
They will still have to graduate to modern parts if they wish to get the speed and versitility that is now availible. Terry