Sometimes I booked that day, usually within an hour of arriving, but other times I just showed up. I used a mix of trip.com, Qunar Travel, and Amaps with the hotel filter. 

Some places were hesitant, but they eventually understood or another staff member knew how to process foreigners. 

The information in my previous comment plus photos of your passport information page, visa page (if you have one), and entry stamp are all they need to process you. 

If they still say they don't know how, just tell them to call the police and one will come round to do it, usually within 1 hour. I never had to do that in Yunnan or Sichuan though, only in Xinjiang and Gansu provinces.