Robert Macy wrote:

It's a PS-2 with a SCROLL wheel and a thumb button along the left
side, plus has the normal two large area buttons on top.

The original label said
Qtronix Lnyx 3D mouse.

Not after scroll function - disabled that.
Not after cable [although would be nice] - been substituting anything
by re-wiring.
just need that pesky little thumb button because there's a program
called scroll.exe that enables this mouse to have a variable size
magnifier to move around the screen.

It's for Ms. Macy's PC, so there is NO substitution possible.

Where can I get one?
I wear out mice and trackballs all the time. I pull the right
button switch (less used) out of old mice and replace the switches
in the ones I use when they go flakey. Usually the left button
goes out first. Almost all mice/trackballs use identical switches
that are transplantable.

Jon