Microsoft MS-DOS 1.25 [Micromint MPX-16]
Released in 1983 by Micromint
For Micromint MPX-16 systems

This is a reportedly unreleased version of MS-DOS 1.25 specifically
for the Micromint MPX-16.

The MPX-16 is a custom 8088 based systemboard that is not really IBM
PC compatible, but includes ISA compatible expansion slots. It
features a built in serial port, and the ability to operate over the
serial port without a video card. It was intended to run CP/M-86, but
was later adapted for DOS. The MPX-16 was featured on the cover of 
the November 1982 Byte Magazine.

This also includes BIOS sources. 

source: http://www.classiccmp.org/cini/systems.htm