I have just purchased a portable DVD player from China (Shinco
SDP-1770, see link at bottom of question), which has S-Video output. 
However, the port requires a mini plug to connect to it, which did not
come with the unit.  I'm looking for where I can buy an S-Video cable
with a 4-pin connector on one end, and a mini-plug on the other end. 
I looked everywhere on-line and also tried Radioshack and Best Buy but
could not find anyone that sells such a cable.  For the answer, I will
accept online stores, eBay auctions, or retailers in the Los Angeles
area.

By the way, Shinco is a Chinese brand and I suspect it might be an
Asian standard to have S-Video come out of a mini jack.

Shinco SDP-1770, see:
http://www.buypcdirect.com/index.asp?PageAction=VIEWPROD&ProdID=647

goetz-ga:

Thank you for your question regarding the adapter cable you need to
use the S-Video Out port on your Shinco portable DVD player.

You are indeed correct in that there is a quasi-standard among Asian
manufacturers to use a 1/8" jack for S-Video, in order to keep the
device chassis size down. The problem is sourcing the necessary
adapter cable outside of Asia, at a reasonable price.

I have found one reputable online source for you, to start with:

http://webshop.fujitsupc.com/fpc/Ecommerce/accstore.jsp

(use the search box at the bottom of the page to search for the
following product number: FPCCBL06AP ).

This is the lowest price online I have found, from a source that is at
least reliable.

I hope that this helps. Please let me know if you require any
clarifications to this Answer.

Regards,

aht-ga
Google Answers Researcher

Great, exactly the info I needed. Thank you!