I browsed for K&N filters on eBay for my Murena 2.2 yesterday and came across a few. E.g. this one (photo is wrong, but scroll down):
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=180370808841(I called "Autobremsen", a local supplier here i Copenhagen, who stocks the K&N range - he would want 750 DKK, i.e. more than 80£ for one of these!)
A K&N may not give you any more HP, but they are good quality, long lasting filters, so I thought others might be interested in this.
PS: I realised this filter is not just for the Murena, but also for the Bagheera and Rancho. Sorry for being Murena-centric again!
Here's the link to K&N's spec:
http://www.knfilters.com/search/product.aspx?Prod=E-9121/Anders