Thanks. You will probably be interested in this info from a VERY helpful gentleman in Sweden.
"I got your email through US Highland and will try to help you from a snowy sweden. Rollox nowadays handles the service and parts for Highland motorcycles, and most of us were part of the old swedish development and production teams. I will help you with the clutch cable but will have to dig in to our old stock for it. However, before I send anything you might find the oil filter at a regular auto shop. Our original filter is a Fram component, PH 5796, and is used in many, however mostly european cars. You find a link to a website below and there you can find some of the car brands that use this. It's been around way back since the mid nineties, so I think this is the easiest way for you. I'll get back to you on the clutch cable since that is of our own design and length. In the mean time - good luck to you!
Other things that might help you are the following.
Air filter: Honda 900 Fireblade -96.
Front sprocket: Husaberg -90-2004.
Rear sprocket: Suzuki DR 600 -96.
Front disc: Husaberg, KTM (Caliper mounts may vary, but pads are the same)
Rear disc: Yamaha YZ 250 -96 (Caliper and pads Husaberg)"
He also sent me a drawing for the cable, which I sent to Barnett, Motion Pro and Terry Cable (thanks PowerCell). Still waiting for a quote from Terry Cable.
He also sent me many engine part prints, if anyone is interested.