Missing planting tool

Hopefully one of those students will pop up and get this to market. I often use a bulb planter if I have small seedlings; with one screwing motion I can excavate roughly the shape of a circular pot. It is exceedingly efficient compared to scraping out the soil with a trowel, a small spade, a hori hori knife, or whatever else. However, its diameter is 6cm. I have seedlings often in trays re-used from garden centres, and their diameters are 9, 12 and 14 centimeters. I'd pay good money for larger bulb planters, say with diameters 8, 10, 12 and 14 centimeters. Perhaps it wouldn't work as well in sandy soils, but on more clayy soil I'm sure they will.
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I wonder if it would be easy enough to make one using a big tin can? They seem pretty sturdy, should be possible to make a DIY short handle planter of various diameters. Put a pull door handle on it somehow maybe...