A broader question might also involve which groups are still inclined to deny the Holocaust up through the present day, and while that might be more of a current issue if you have any insight into the development from immediately after the holocaust until now, that would be very helpful.
Hi, while you're waiting for a direct answer here, you may be interested in some earlier threads on the subject:
/u/commiespaceinvader describes the beginnings in When and how did Holocaust denialism start?, then gives a historical overview in How prevalent is Holocaust denial and how does it vary by nationality?. You may also find this of interest From the mid-80s onward, many countries (such as Germany, Israel and France) made holocaust denial illegal. Why did this happen such a long time after WWII? Were there any earlier attempts to outlaw holocaust denial?
commiespaceinvader discusses on denialists in Monday Methods: Holocaust Denial and how to combat it
/u/kieslowskifan comments on denialists in How do you instantly shut down Holocaust denial?