Or use a standard 5-frame nuc with a follower/block to limit to only 4 frames. Take the follower out as they expand and need a 5-frame setup. That said, I am moving to all 4-frame nucs that can double up on top a split 10-frame deep or under a single telescoping cover.
if you're somewhat handy with tools, you could pretty easily make some nucs.
or you could go the route that i did last winter and divide a deep box in half by adding a 1/4" piece of some sort of plywood material in the middle of the box. take a circ saw and cut a groove in opposing sides on the deep box just wide enough to hold the plywood. voila you have 2 4-frame nucs out of a deep box. when spring time comes, and you want to move them to 10-frame equipment, remove the divider and get your deep box back.
edit to add the image below to better describe what i'm talking about.
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