I've figured out how to request an individual article via ILLiad, but what about an entire issue of a journal?
I'm afraid that it is not possible to request an entire issue of a journal with one ILLiad request. The best way to achieve your goal is to place separate requests for each item (article/paper) in that issue.
If you are able to see the abstract for each item in that issue, through the journal's website for example, that should give you an idea of everything that is in the issue ...and from here, it should give you the information you need to place those requests. Using cut and paste could speed up the process.
Sorry if this isn't what you were hoping to do!