I think the best bet is for you to acquire another SGI machine, unfortunately. There are several open source MIPS emulators but their functionality does vary.
Available emulators include:
Update: Newer releases of MAME are now able to run certain releases of IRIX, emulating an Indy. Instructions are available on the IRIX Network Wiki.
As far as I am aware, there is no fully working emulator for SGIs, because the graphics hardware consists of custom chips, is not properly documented, and hasn't been reverse engineered yet.
Also, the disk images that would be needed to run an emulator are still under licence.
There is some code in Mame, but I think this is work in progress, and I haven't ...