Try Einhell UK Ltd on 0151 649 1500
www.einhelltools.co.uk
The Nylon Gear is the same on the Spear & Jackson Chainsaw SPJCS - 1840.
http://www.einhelltools.co.uk/product-list.php?pg1-cid1959.html
Its called 'Output Shaft Assembly' Part no 450156302097 £21.53 inc Vat + postage
Best of luck
Surrey Log Man
March 2017