i have no real clue... but i'll take a stab at it anyway.
if you're set on it being anonymous, exactly HOW anonymous do you want? i mean, you could find a glory-hole in an adult shop and that's about as anonymous as you can get.
OR, if you want to be safer about it, you could see if you could find someone you trust to arrange something for you. they could either find a willing participant who's not part of your circle of friends or you could make your own glory-hole box and be concealed from whomever is rounded up for you.
if you're just looking for it to be anonymous in the sense that the other guy doesn't know you but can see you, then i'd say go to a gay bar/club and see what you can find there. if the scene turns you off, you can always leave having given it a shot and just leave it as a fantasy.
I had great success meeting online a few times. A great gaysite locally in our city to meet and chat. I strongly recommend chatting several times to build a a rapport and a confidence then meet neutrally.
You will see the game players or the creeps pretty quickly. I just brushed them off or stopped chatting to them.
honest guys are more than willing to partake and take the time for a willing but nervous.shy newbie. That has at least been my experience.
meet up. if you feel trust, go off somewhere private suck etc. then go your own way. real names aren't even necessary. good idea to play safe of course.