Jumping out of second gear

[Triggergee]

I stopped using the bike when it developed the problem so no more damage is being done, I didn't realise a nackerd chain can do so much damage I thought it just feels horrid. As for 2nd gear, as soon as I release the clutch and start accelerating passed 3,000 revs or so it jumps out of gear into netruel. I've managed to get hold of another drum but can't find a set of forks, Ebay has a pair including the right and centre forks but no left fork