[Milsurplus] Making mold for parts

[John Hutchins]

List -
What I have:
Unit is a HP8601A  with all sorts of USAF Mil Lab stickers and plates, 
not a unique
piece milsurplus unit, but it has papers }.

The Problem:
I have a lighted push button switch cap missing.  Presently I use a #2 
pencil  eraser end to
turn on and off the unit.  I have searched the web for, a replacement or 
new lighted switch,
 or a replacement cap.  No luck.

My Thoughts:
Thought of  paying a few dollars for a junk unit to strip out the switch 
has crossed my mind;
 But! -here is where trouble starts-   If I could make a mold and pour a 
plastic casting:
    Economically - the create your own mold might not make sense but 
would be a interesting
    project, that could prove valuable later.

Need your Feed back:
Conceptually this seems simple, but I have been there before; and it was 
not pretty:
Any Comments, has anyone attempted to make a mold?

What materials would I need to make a simple mold for a small plastic part?


Thanks
Hutch