August is the worst month to find anything for rent in Spain. The rentals' prices are much higher at that time in tourist zones like Asturias.
I would look at online sites like idealista.com .
If you find something interesting you can contact directly with the owners or the rental agency and ask them the details you want.
It will be easier if you can ...
While Mark is right that as per guidelines you are not required to present accommodation proof in the embassy. Still, we don't want to take chances. So what I did. I did Six bookings from booking.com, for one month each. For example:
First booking from June 1 - June 30th
Second booking from July 1st - July 31st and so on ...
If I wanted I could have ...
I assume you mean the registration of your residence, which is not the booking of a hotel, but the renting of an apartment after moving in.
Read Step 1 of the link below
the issued Meldeschein is the proof that you need to show the Ausländerbehörde
resident permit - What are the things I should do after getting into Germany?