It's OK (although not ideal) to cite one author from another's work if you cant get back to the original source, as long as you reference it correctly so that it's clear that is what you are doing.
Example:
"Smith (2004) states that Jones (Jones 1998 in Smith 2004) has resolved the issue."
If you didn't have access to the original Jones 1998 text, you would cite in-text as above and put a full reference to only Smith 2004 in the Bibliography.
However you should try to avoid doing this if you can. It isn't great technique, but sometimes library access limitations and coursework deadlines don't allow time for inter-library loans and it's necessary. Keep it to a minimum though and if in doubt, ask the person who set the assignment for guidance. There could be guidelines for this at your uni, or the person setting the work (and therefore marking it) may have a personal preference one way or the other.