Using latest version of tincymce (4.3.3), it is looking for theme+skin under /bower_components/tx-tinymce instead of /bower_components/tinymce
I tried editing tx-tinymce.js to add to config:
theme_url: '/bower_components/tinymce/themes/modern/theme.js',
skin_url: '/bower_components/tinymce/skins/lightgray',
Seems to have fixed it, but I think there is a better way besides hard coding bower_component paths into config.