Barts spices do an Harissa which is relatively mild if you buy the Alfez brand it is a little hotter. Also you might find the Belazu Rose Petal harissa which is divine.
As always with spice blends add a little and taste as you go. I made a homemade batch recently and it was eye-wateringly strong, I knew I was going to need an industrial quantity and thought it would be more cost effective to make it myself - it's going to last me a very long time as a little goes a long, long way!