I don't think you can be held responsible for other peoples mistakes.

I would hope that the chips would ultimately be returned to you in which case you could send them to the buyer. I would let the buyer know that otherwise he is out of luck.

You might ask if the old address is near to where he is living now, he might possibly be able to trace them that way.

I don't think that shipping should be either a revenue producing item nor should it be used to cover ebay fees.
As a result, I charge $2.30 for shipping which INCLUDES insurance.
My padded envelopes cost 12 cents, Insurance is $1.30 and 88 cents should cover postage in most cases.

I doubt anyone would complain about $2.30 for shipping