I recently obtained a personal IRIS with a complete documentation set, circa 1990/1991. I'm in the process of scanning everything and getting it uploaded to bitsavers. I checked SGI techpubs and all the IRIS GL and older IRIX documentation does not appear to be on there. If it's already online from SGI techpubs, I'd like to know that since they have PDFs generated from source and not from scans.
Completed scans are in http://bitsavers.org/pdf/sgi/iris4d/
I publish an RSS feed
for bitsavers so you can use that to get notified of new documents as they appear. (Look for category 'sgi'.)
Of particular interest to developers will be the FORTRAN documentation and the IRIS GL documentation.