Maybe a Microsoft employee could give some hints?
Anyway, Id start with the Microsoft CEO. Id even email Bill Gates - he would have to"have some sway" if you could get his support - maybe internally ...?
May be the old authors of the software could request it be released.
Is it know who the authors of the ROM was?
OR
Even other hardware designers / workers who worked on original system - would bring interest to Microsoft and have to have some kind of positive momentum to such a request.
Is it possible to work out the reasons how other old Microsoft software was released ? I imagine there would be reluctance to release anything that they thought had commercial value?
As several products have been released over the years - there must be some offical or unoffical process
Legal would have to have input
I imagine there would be some close examination of software to verify , no negatives against Microsoft would / could he harboured in code OR found.
So it would take some resources - maybe several days as a guess - but I really have no idea ... For example probably would want to verify it can be rebuilt - maybe?? would need to setup old toolchains , old hardware etc
Also Some of these software may have been lost - could be embarrassing for Microsoft to admit this.
{Aside - I used to work as a software configuration manager for a larger company - whose job it was to ensure all project code was collect, ensure we capture all the artifacts ( source and deliverables etc ) so it could be reliably independently rebuilt. This included all needed tools etc etc]