Is this your bike?



If it is, the bike shown in 1986 will have standard British parts. The handlebar diameter at the clamp should be 25.6 mm.

The helicomatic is a potential problem, because they are no longer being made. To replace it, you would need a different rear hub or wheel. If it's still good, and you just need a lock ring, you should look on EBay.

By the way, I have the Corbier model. It is a nice bike to ride despite being at the bottom of the Peugeot line.