submissionary

I don't believe that that is a word. Is this from a source written by a native-speaker of English?

Yes, and actually, it comes from a dialogue in a textbook, the word "submissionaries" is used, and according to the context, "submissionaries" is the name of a band. I really want to know what this "submissionaries" means.

Saying that it is from a dialogue in a textbook is not evidence that it was written by a native-speaker of English. We've had some really awful examples here of textbook English which was not in fact written by native-speakers of English.

If it's the name of a band, it's just made-up. Submissionary doesn't mean anything.

Your explanation really makes sense, and I agree that it is just made-up, since it is only a band's name, thanks a lot!