The one I usually do Midscreen is 5AA>2B>j.a>236A>236236[C]>214214D [C]. I usually input Circus Bear as soon as I land, hold C until I see the missile, release C to let the explosion hit them, and they usually fall into the circus bear regardless. You can also use it to tech trap, but this is what I do for a guaranteed hit to make it a legit combo. I haven't found anything for the C version, but that's my go to one for the D version.
It can also be done in the corner after D Missile, but the timing is short of strange. But you can do 5AA>5B>sj.c>j.b>j.a>5B>5C>2B>j.a>236A>236236[D}>214214D. From what I noticed, The very start of the explosion hitbox has to hit them. So do it as early as possible, making sure the explosion hits them and you get circus bear to set off. They will be able to tech if you did it too late, but if you did it right, it will also be a legit combo.
This is assuming that you don't care if Tomahawk is used to achieve this. But yeah, those are just 2 ways to combo into circus bear without items. My explanation may look a bit off, but that's the jist of 2 of the practical ways you can combo into Circus Bear without items.