Fantastic!!! Thank you so much for your help!!!
I had already tried putting the fonts into editor.css but it looks like $contentcss is using the editor.css in the base theme for the editor rather than the current theme.
I did this in /lib/editor/tinymce/lib.php in function get_init_params()
$contentcss .= ', /theme/mytheme/style/fonts.css';
$fontselectlist .= ';Aka Dora=akaDora';
And in /theme/mytheme/style/fonts.css
@font-face {
font-family:'akaDora';
src:url('/theme/mytheme/fonts/akaDora.eot') format('eot'),
url('/theme/mytheme/fonts/akaDora.woff') format('woff'),
url('/theme/mytheme/fonts/akaDora.ttf') format('truetype'),
url('/theme/mytheme/fonts/akaDora.svg#akaDora') format('svg');
font-weight:normal;
font-style:normal;
}
Purged the caches and it works! :D
I still need the @font-face in /theme/mytheme/style/custom.css too so the content is displayed correctly but I'm just thankful to get it working ;)