How do I get the handcuffs in the London event?

If you merge 2 of the theatrical hats it gives you the Skelton head with a crown which foes to the theatre curtains this then gives you a crown which you merge with the monkey and you then recover the crown and merge that with the case and its rewards you with handcuffs

Create a crowned scull - give it to the ape and the ape will provide you with the handcuffs.