Visa Validity - PLEASE HELP

I am doing some travelling (departing Mid April) and am planning to visit China for a few weeks in August, I have read that visas are only valid for 3 months from applying and was wondering the best way to apply as I will be leaving the UK in a few weeks for SE Asia so applying before I leave will mean this Visa has expired by the time I plan to get to China.

Am I able to apply for a longer visa? or maybe in another country on my travels closer to the time? Can't seem to find any information on this anywhere so any help would be much appreciated - THANK YOU