I'm doing the final proofreading for an article due for submission tomorrow and I have realised I have missed off the page number for a footnote reference. I don't have the book anymore (obviously) and I can't get hold of it before tomorrow. Should I make up a page number, just leave it blank or do something else - if there is an alternative option?

I'd leave the page number off.

I got some missing page refs by searching for relevant text in Google Scholar. Also, Amazon happened to have a scanned section of a book I wanted for another last minute reference.

Failing that, would it make a huge difference to the article if you took that clause out or rewrote it to get rid of the need for that page number? Would your conscience bother you if you made up a page number?

I know it's not the same, but I lost both my copy of a book I used and my written notes that I really needed for page numbers for a couple of references the day before I submitted my thesis. I left the book and author reference in but without page numbers in the end, in the expectation that would go on my list of mechanical corrections as possible typos. Probably a bit sloppy in a perfect PhD world, but it was the choice between submitting it or not, and it wasn't going straight off for publication.

perhaps it depends upon how important it is to the article. If it isn't that important leave it out, if it is important can you reword it so you don't need the page number, if not, leave off the page number. I'm assuming this is just (!) for a first submission, in which case it might come back asking for the page number, by which time you can find it ready for putting in.

Has the article been through the copy-editing process by the publishers yet? If not, you'll still have time to add the page number when you get to the copy approval stage.