This thing might work for you! Depending on how far you place it from set it might be easy to have a 1” circle. You may need to drill your own “graphics card” to get a really specific size circle projected.

Note that I’ve only used similar products from other, pricier manufacturers, so I’m not familiar with the exact functionality of this one. Just guessing you don’t want a Profoto modifier that costs more than your AlienBees strobe!