This is the website that I use to order Spanish certificates. I am slightly confused though because I can never find Corella as a Registry Office in the lists.
First the Region:
Next, the Province:
Then, when filling in the details for the certificate you choose the Registry Office:
As you can see, Corella is not listed! But I have checked the official maps and Corella falls within the overall Tudela area:
So I can't work out how to select Corella as an office location. The original links for ordering are advertised here.