Now while I understand that sissies are not the cup of tea of every gay bro out there, I think it would be silly not to include a few destinations where are more 'out there' allies visit when they want to get down and dirty. /r/Sissies is a good subreddit for exactly this and as far as I'm concerned, it's a top pick if you're interested in seeing guys turning themselves into little feminine sluts.
I recommend hitting up the 'top rated' section and sorting it by 'all time'. What you're going to get is a whole list of some of the best amateur sissy material the Internet has to offer. Note that /r/Sissies is 90% self-submitted porn, so you're going to get users of the site that you can interact with and make requests from. Anyway, it's all about having some fun and if you think you might be interested in becoming a sissy yourself, feel free to reach out, grab some panties and post your ass parading them around.