Use this site to source the part numbers
http://www.alpha-sports.com/suzuki_parts.htm
Click on the year then your model
Use this site to check prices
http://www.robinsonsfoundry.co.uk/
click on the parts section in the on-line shop
I've been getting my oil and filter from Hein Gericke as they've been doing a deal that gives you 5ltrs of 10/40 semi, oilfilter and airfilter for £24.50. Bargain. However I believe they've stopped that deal now. Bu**er.