k818c is a chinese version of the K810. so you won't find those firmwares you want

you can flash to the regular K810. the firmwares (i asume you have CID52) can be found here: Downloads - R8BA024_RED52 - Top Sony Forums

edit: acces to download area is not free, you will have to pay for it. or ask free acces when you are more then 1 month member and have over 10 usefull posts