It is very difficult to improve speaking ability without either a language partner, a teacher, or a classroom. You can take your writing, reading, and (to a lesser degree) listening skills to a fairly high level without ever talking to a native speaker in real time, but I don't know of any way to get really good at speaking totally on your own. In my experience, speaking is the most difficult of the four skills to master -- even with conversation partners.
My advice is to keep trying to find language partners via iTalki, or whatever platform you prefer. It is a little like dating, you won't "click" with 4 out of 5 people but the fifth one may take you very far.
I hope this helps!