You can probably go even further back and get an Extra manual from the 1970s. These don't have the question pool answers, but they do have a wealth of knowledge that should help you understand the material well enough to get those questions right.
I disagree. I have the 1970s guide and the 2008 guide, and passed the extra in 2008 (Advanced in 1974). The modern Extra test has many questions about satellite, ATV, EME, new regulations, logic circuits, that are not mentioned at all in the 1970s guide.