Your best bet for a new key fob would probably be Ebay.
As far as I know you're looking for a 315MHz one, not 433MHz. Hopefully someone else can confirm that.

 

I purchased a 315 MHz one from Keyecu at Amazon.com, it was listed as "Keyecu Replacement Flip Remote Car Key Fob 315MHz PCF7941 for LR3 Range Rover Sport 2005-2011 FCC ID:NT8-15K6014CFFTXA". If you are not in North America, you may need the 433 MHz version, in which case you'll have to investigate further...

 

So are you guys just taking out the existing boards and blanks and swapping in your already-programmed board and existing key into the new housing?

I was going to just buy the empty shell:
And a new battery:

 

You have a choice, either buy a new not programmed fob and move your PCB and key over to it or look for an empty fob case and fit your PCB and key in it. The later may be cheaper as you won't be paying for a PCB you're just going to bin.
Do be aware that moving the key over sometimes can be a problem, not a big one, but you could find that the button and blade in your old key don't just fit into the new case. You then have to detach the blades by removing the small roll pins and swapping yours over and securing it with the pin.
See my original post on this as I detail the procedure and have photos of it too.

 

I did it both ways, bought 2 empty cases and transferred the electronics and keys, plus installed new "solder in" batteries, and also bought 2 unprogrammed fobs with electronics/batteries/blank keys. The keys had to be specially cut and I had to go to Edmonton (about 90 miles/145 Km) to find a locksmith who scroll cut the keys but I programmed them myself with the IIDTool. All 4 keys had to be present for the programming, and now I rotate them every month, when we go to the mountains we always take 2 keys with us. As others have posted, this is NOT something you want to go to the dealer for, their prices are approaching $500 per key...

 

Got it, thanks guys. Will go for the empty fob route initially and see how that goes. An empty non-LR branded fob is like $8 on Amazon so if it doesn't work out it's not a big deal.

 

What? What a rip off. Here in the UK the equivalent is (£180) $243.43 inc. tax and I thought that was bad.

 

Yes, in Canada and likely Australia, prices are through the roof for Land Rover parts, I get electrical things from Rock Auto in the USA...