Hey, Alan, @Stephen Silver does 30min 1-on-1 mentorship sessions through Skype. You can arrange directly with him what you'd like to discuss, whether it's portfolio review, career advice, artistic goals etc. I had a few sessions with him in the past and found it helpful. Stephen is very friendly and generous with his knowledge and experience. Of course, a portfolio review is best when done by an artist from the same niche you wish to explore. Stephen is a caricature artist and character designer who works majorly in a cartoon style, so if that matches your preferences, a 1-on-1 session with him could be a suitable option to consider. He displays more details on his website: https://www.silvertoons.com/1-on-1-mentorship Hope this helps.

Sometimes there are portfolio review events at comic conventions! Online, it might be worthwhile to reach out to professional artists in your niche (asking if they're willing, of course!) Other options could be forums, like here or places like Reddit or Discord communities based around art. The quality of feedback may vary though!