I have casino affiliate accounts which generates me average $1200 per month. I'm willing to sell them for my next 6 months revenue. Is it possible to sell these accounts?

If you can change the account information yes you can sell pretty much anything...

Usually people sell their sites, not their accounts in affiliate programs.

And in most cases this is also forbidden by the affiliate program.

I was in the casino aff game for a few years (got out in 2007) with the advent of the UIGA and I would be very surprised if your aff managers would allow your account and "clients" to be transferred.

Discuss the possibility with you affiliate program manager, he can tell...