I am looking for a replacement lock mechanism for a horizontal,
double-glazed, sliding window; the broken part is a 2-piece, riveted,
pivoting mechanism that "nests" in a groove on the stationary half of
the window when latched; it is stamped with the name "Western
Products".  Any idea where I can find one?

You could try to contact the manufacturer for advice on where to get
replacement parts:

Western Products
117 23rd Street North
Fargo, ND 58102
--
Phone: (701) 293-5310
Phone (toll free): 1-800-743-3632
E-Mail: info@westernproducts.com
Website: http://www.westernproducts.com/

Regards,
Scriptor

Thanks for the info, Scriptor.

You could also contact Blaine Window Hardware at 1-800-678-1919 or at
blainewindow.com.  I sell windows and doors, and have used them many
times to find those "hard to get" items.

Good Luck!

Thanks, jthompson! Blaine Window did indeed have the part I need;
also, as you say, they appear to be a great resource for all kinds of
door and window hardware.
Thanks again for your assistance.

Best regards,

arjay