Please find out how to acquire a replacement "white plastic top" for
my Omega Juicer 1000.  (I can't find the company home page or even a
phone number.)

OR 

Find out if I'm just supposed to buy another juicer because no
replacement parts are available?

Dear donphiltrodt,

You can order the white plastic top, and many other spare parts for
the Omega 1000 Juicer, directly from Omeca Products, Inc. for $19.95.

This is the part of the Omega website where the part is offered:
http://www.omegajuicers.com/item.cfm?item=26

Here are the other spare parts available for the Omega 1000:
http://www.omegajuicers.com/category.cfm?cat=4

Here is full contact information for the company:

Omega Products, Inc.
Harrisburg, PA 17111-4523
Phone: (717)561-1105
Fax: (717)561-1298
E-Mail: omega@omegajuicers.com
Website: http://www.omegajuicers.com/

Search terms used:

"omega juicer"
://www.google.de/search?q=%22omega+juicer%22&hl=de&lr=&ie=UTF-8&oe=UTF-8&newwindow=1&start=10&sa=N
"Omega products, Inc"
://www.google.de/search?q=%22Omega+products%2C+Inc%22&ie=UTF-8&oe=UTF-8&hl=de&btnG=Google-Suche&meta=

Hope this helps!
Best regards,
Scriptor

Perfect.  The direct link to the product was especially convenient and
made for a very positive GA experience.  Thank you.  Had I priced the
question lower, this answer would certainly garner a larger tip.