go to yard sales specifically looking for classic rock albums? I used to do that all of time. Not so much these days. There is a used record shop not far from me so I have been doing that recently.
I look for classic rock CDs, you can get them at some yard sales where the usual price is $1 which is a lot less than the used album stores charge for them. Problem is you rarely know what type of CDs they have, they could be all classical music or polka or religious organ music, etc. But I still enjoy the hunt.