Is there an actual portrait of John Cleland anywhere?
When I came across your question, I was immediately intrigued by it. I find it very curious about authors and the existence of the author's portrait. After an exhaustible search, I found only one place that claims to have a portrait of John Cleland.
The portrait is found in a German publication of under the title Memoirs of a Woman of Pleasure. Memoirs of Fanny Hill.
The text was published in a hardcover edition in 1923. It was published by Bertelsmann's Gütersloh. While I could not access the book on-line, the site I found selling the text (Amazon.co.uk) has the book priced at $27.30 US dollars.
If you would rather, I would suggest trying to get a loan through your local library. The call number on the text is ASIN: B0014XOC92.