I have a NCC Inc. Timer Model 28011. Two (2) of the outlet covers are missing hold-down springs. Where can I obtain two (2) of those springs

Try contacting NCC to find out who sells their products:

Welcome to The NCC (http://www.thencc.com/ncc/contact.html)

Or try the number on the instruction manual:

http://www.thencc.com/LS/Instruction/28011_Manual_2007.pdf

Or try a local hardware store to match the missing springs.