looking for method of inserting Amazon data into php form

looking for method of inserting Amazon data into php form

I have been looking around for help trying to fix my old system of
inserting returned search results from Amazon into a form.
The way it worked was I have a PHP based form for saving book information.
The user typed in the ISBN and clicked a button, then a JavaScript program
generated a signed request that returned the data in XML form. The JS
program used an xslt file that converted it to a json type of results that
then was inserted into the form fields. The reason it all stopped working
is Amazon stopped supporting any xslt requests to their server. I have
been able to substitute with googleapis, but I would rather use Amazon if
possible.
I need to find out if anyone knows how I can do this now. My code to
generate a signed request still works. I can make tests that send out a
request, and I can see the correct XML response by using Firebug, but I
just can't figure out manipulate the returned data the way I need to.