Key wont turn - ignition barrel

[bunker]

As it says really 

Was getting ready to fire the old girl up last night to see how these newly rebuilt carbs would run, but the key is in and won't turn.

TBF I didn't have a lot of time to look very much further than spraying some GT-85 into the barrel and giving it a gentle tap on the bottom (no sniggering at the back!).
Is there anything I should be checking? I'm guessing the barrel comes apart easily enough, but if its knackered will one from another model fit? (had a quick look on ebay and there seems to be nothing on atm)

Thanks guys 

[threepot]

Can't comment on this one,but seems plenty of info if you do a 'search'??
Apparently not easy to remove due to 'shear' bolts😕

[Nick Calne]

Don't forget if you change the ignition the key won't match the tank or seat. Might be better getting a complete set.

Also 3pot is right there is something tricky going on with the ignition barrel fitting. You can't just unbolt it if memory serves.