UK Ciziten requiring visa to last for longer than 3 months

Hi my husband and I are travelling around Australia, New Zealand, Vietnam Cambodia and Hong Kong and China this will last 4 months - our last place to visit is China - however we will be out of the UK for 4 months before therefore we will need to apply for a visa before we leave the UK - is there a way to get an entry permit that last longer then the 3 months - if not how do we get our entry permit to China when we are travelling ?