I've been looking for more outlets for the whole "cock steadily getting larger up to and beyond the point of completely impossible massiveness" fantasy I've got as it's my main kink. Roleplay's always fun, but it's hard to find good help these days.
Can understand how you feel, mate.
Have a similar preference in roleplays and really no one who is into it or is good at it.
Hope that you can find someone who can help you out.
As for the topic at hand, all the major sites have been listed by sometimes sites like literary erotica has growth stories.
Just a pain to go look for them amongst everything else.