is there any way to get a Visa which will last longer than 90 days before expiring

I am a UK citizen and was planning to leave the UK in late July and then travel through Europe and Russia before arriving in China in November (I am going to catch the Trans Siberian). But if it will only last for 90 days, then it will have expired while travelling...

Is there any way to pick up it in July that will be valid until November?

Or can I pick up mine in Russia or Mongolia?