I would analyse the text like this:
"And when such as had come in contact with Strickland in the past, writers who had known him in London, painters who had met him in the cafes of Montmartre, discovered to their amazement that …"
And when people [writers in London, painters in Paris (Montmartre)] that had known Strickland in the past discovered or ...
Adding to petitrien's explanation: there is here used as the subject of the verb appear, a copular verb a special kind of verb as be.
There began to be rumours. (There were more and more rumours.)
There began to appear (...) a succession of articles.
I don't think your break-down of the sentence is correct. I understand the sentence in the following way:
When people who knew Strickland in the past realized he was a major artist, they gave interviews about him to journalists and articles bagan to appear in the press.
The sentence can be reduced to something like this:
And when such as had come in ...