www.petandortoiseworld.co.uk sell fake plants, although their website seems to be undergoing some sort of remodelling at the moment and the "plants" section isn't displaying properly. I agree with Jacqui though, real plants would probably be better. Visit www.thetortoisetable.org.uk for a pretty comprehensive list of tort-friendly plants and pick a couple that take your fancy. You don't even need to take them out of the pot - just partially bury it in the substrate and let the leaves hang down to create a hiding spot.