I have seen the recipe five times in the last five or six days, but zero times in the first four or five days of the event. But in the actual thread about the event, Marindor confirmed the recipe will be active for two weeks after the event ends.
i've got twice during event, i don't use because there's not enough artifacts to make logical ammounts of old ones anyway.
I've got moon bear and after rebalance i'm using him.
I have only seen the artifacts in magic academy twice: the first time on the first day of the event, and then again around quest 22 when I got the 2nd bear artifact. I got the brown bear in magic academy instead which was also on offer the first day but since then nothing. No artifacts no bears. So not so frequent...
Got the brown bear at level 2. Its good for troops but a waste of artifacts if you cant get it to 10.