>>>  Does anyone know where I might be able to get a copy of DOS 3?

Used book stores, garage sales, educational institution outlets,
Library book sales, computer clubs, friends. . .

I've gotten full DOS packages from these sources -- disks, licenses
and manuals -- either for free or usually for a $1. Usually you see
IBM PC-DOS 5.0 which works fine on true clones.

Try school outlets. They all went to Win95 (and you can also get their
old 286/386 PC system units, usually for $10).

I wouldn't get anything less than DOS 3.3 (fits on one 1.44MB disk). If
you have HDD over 32 Megs, you need 4.0 or higher. I recommend
DOS 5.0, comes on 3 x 1.44MB disks.

And to be honest, I would get a 386DX. The motherboards are
thrown away (if upgraded) or sold for a few dollars (new). You wouldn't
want to use an PC-XT HDD but a 100MB IDE drive is $10-20 (new)
if you can find them.

Regards,

John Chin