The last
release of SunOS to support 68K ("sun3x" kernel architecture
 for the 68030-based machines, the 3/80 ad 3/400, all others are "sun3")
 is 4.1.1_U1.  I have boot tape images, but not a CDROM image.  I don't
 think I've ever seen it on CDROM for 68K. 
 If memory serves, it's still on the CD-ROM alongside SPARC, if you know
 where to look. I don't have my SunOS CD-ROMs with me to check, though. 
 
    They certainly weren't on the SPARC distributions, at least not the
 4.1.x series.