We'd both bought some filter material being sold by Ramair on Ebay. The packet contains two sheets of double layer filter material, enough for 8 Skorpion filters, for only £10.
These were being sold on Ebay as '2x RAMAIR Air Filter Foam Large Scooter Motorcycle Quad' as clearance, so if you want some, buy sooner rather than later. I'd made a DIY filter for my own bike so here's a Blue Peter style 'here's one I made earlier' picture, along with a used standard filter.
Fit to bike and give it a test run. If (and it's a very unlikely if), the bike needs rejetted, then that's something you'll have to work out for yourself. Frankly, I seriously doubt you'll need to do it unless you ride flat out all of the time.
When it comes time to replace the filter, use a heatgun to melt the glue and pull the old filter out.
It should be possible to do this using any available filter material. Using a car K&N filter has been covered on my website, but I would imagine a piece cut from any suitable car or bike airfilter would do. I've even heard of someone using a green 'Scotchbrite' pot scourer, but that's not something I would personally advise!
I'll report back after I've done some distance on my Skorpion, and if anyone else does it, please let us know.
Disclaimer: Done at own risk...blah, blah........don't blame me if your bike blows up......blah, blah.......knives are sharp, so don't cut your fingers.......blah, blah.......glue guns are hot so you could burn yourself.....blah, blah.........