The other option is a 22.5 litre tank from Brazil that is much cheaper than the off-the-road offer. However, it is stated as being for the XTR (link below), but there is a Guy on Advrider (and here?) that has installed one on the X.

http://www.gilimoto.com.br/index.php...&product_id=86

The owner, Giovana, speaks/writes sufficient English to make the transaction and delivery should you go that route. It cost about �330 (plus customs) delivered to London. Delivery took a couple of weeks.