I've attached images of two mice.

I have several Kensington mice. Model 72121.  It's the perfect mouse for me,
but it's no longer manufactured.  The 72121 is a 5 button mouse, but notice
there is only one large thumb button.  All the new mice I've looked at have
two or more thumb buttons close together.  Most people must be comfortable
with this new design, but I'm not!

The other image is a model not common in the USA.  It's sold mostly in Europe.
It's called the Rockfire 4-Button Optical Mouse.  There were exactly two Google
listings for this model (RM-802).  One business was destroyed in a flood and
and the other no longer stocks this model.  Notice it has one thumb button, like
my old Kensington mice.
 
I'm tired of searching.  Can someone help me find a 4 or 5 button mouse with
one thumb button?  I really PREFER corded mice, but I'll accept a wireless model.
Please, no "mini-mice" that are frequently used with laptops.  It must be a full
size mouse.

Thanks guys.

[attachment deleted by admin to conserve space]Sod you must have already seen this:
Unusual Computer Mice You Probably Haven’t Seen Before
You MAY already know a Multi-Button Mouse is sometimes called a 'puck'  used in programs like Auto-Cad. However, it is now hard to find them.
Image from eBay:
That has five button if you INCLUDE the wheel.
Also, the model you want is on eBay.
Kensington Model72121
Does that help?  I apologize Geek-9pm and to all forum members.

I'm a partner in a business and things got kind of crazy for a few days.
That's why I didn't return to this thread until today.

I checked eBay and many other sites dozens of times, hoping that someone
would have leftover (but new, in the box) Kensington 72121.

I don't want to buy one 72121 that some guy found in a junk box.  That's
the kind of stuff I was finding on eBay and a few other sites.

I'll download several pdf catalogs from mice manufacturers and try to find a
good substitute for my old Kensington model.Hope you find the Kensington 72121
As you said, it is not in production.
Amazon lists it as currently unavailable. It may be worthwhile to contact them directly and put in  a request.
Kensington 72121 on Amazon
The customer reviews indicate it was solid in 2013.