As it would be the first time for me to sell my Bitcoin, I have no idea if existing brokers on the market are willing to do such thing?
They don't care whether or not you're a newcomer. Exchanges not allowing new registrants is nothing more than a sign of incompetence. On top of that, I don't think people should be bothered by Bitfinex not allowing any new registrants anymore. It's not an exchange I would recommend. If you are looking for solid exchanges, then go for Coinbase, GDAX, Bitstamp and Gemini. I must however point out that while Coinbase might be the main service nowadays for newbies, it's quite expensive if you are a high volume trader due to their higher fees. If you're just an occasional buyer and seller, it's not that much of a problem.