Almost no reason to sell 0-days on the black market anymore if you can broker it to security firms. Risk is high and chance of being ripped off is crazy high when selling on black market. Another plus being that 0-day sold to reputable security firms can land you a 6 figure job.
Isnt that exactly what I said anyway a decent remote will land you a six figure one time paycheck... The OP wasnt trying to sell for/to the blackmarket, he is trying to get bitcons for bugs, rather than usd. so he can remain anon - a lot of background checks are done by pentest companies. 3com and idefense are useless, more than useless and a rip off. as my experience with another very vocal member of the security community.. there are few pros like 3APA3A around anymore. do not use them. but then I was never a scene kid.... those that can do, those that cant talkabout it.
as a tip, look at using beyond security, they are good people - contact them first with your 0-day. then there is argensis they are also trustworthy lastly try NGS, none of these companies are shady and will pay 6 figures for the right bug.
anyway, seeing as you have so much experience in this (please dont be skylined - and yes I know why you are called skylined, so no bullshitting, you still owe me a pint!!)
good luck.