is a link to Splinter Cell on eBay.Here
is a complete kit on eBay. Not sure which softmod it uses, but you can download HeXEn to upgrade your softmod after installation.
These are all in the UK, but you can change the search criteria (under Location, in the panel on the left of the eBay screen) to pick a country of your choice. Just make sure it's a country that uses PAL TVs so the game will run on your Xbox.