I suppose all DJ mixers with send/return are stereo. Most are not “small” and definately not cheap. A filtered list at thomann:
Otherwise the very small (recently discontinued) patchblocks pbmix3, though it has no aux faders: https://ask.audio/articles/review-patch-blocks-pbmix3
If you have infinite money: schertler arthur: http://www.schertler.com/en_IT/configurator/arthur-format48
A bunch of rane sm62s can be anything you want.