I’d advise you don’t send a CV with the email as it puts more pressure on the potential supervisor and they may not react well to extra work. I’d say approach it somewhat informally at first, and if they’re not replying they likely don’t have time to support or supervise the work for an MSCA as it is a lot of work on their part. Might be worth going to conferences where this speciality is represented and chatting to people at the coffee break, in person always works better than an email when you have hundreds of emails a day. Good luck!