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.