re: "Hello everyone, is it possible to form a group or community of Transcriptionist ? so that clients can easily contact us instead of interviewing individuals?"
The purpose of the Community Forum is not to allow clients to contact you.
Upwork already has search features and browse pages for freelancers in various categories, including transcription.
Hey Joseph. I know what you are getting at, and here is the only solution.
The best option would be for a transcriptionist that is a "Top Rated" Freelancer on UpWork to create a Transcribing Agency. It's a good idea, and for clients that are looking for a variety of transcribing work, having multiple transcriptionists in one place would be beneficial.
If you aren't "Top Rated," work to get there and open one. I did the same with a writing agency (finding out that, sadly, the "Writing Agencies" were not "really" angencies, but writers under an Agency name which doesn't accomplish anything). So, I changed that and am in the process of growing mine (and it's done very well so far).
Keep your head up, and take your idea and make it your own. You're on to a great idea, honestly!
Hope this helps,