This Kessler Crane part would fit the Junior receiver and has a 3/8" thread at the other end. A version of this with a plate may be available off the shelf. If not, I don't imagine that it would be unreasonably expensive to have one made:
EDIT: What gives me pause about pop-up Baby Pins on Combo stands is that the Baby Pin is offset from centre. However, some stands with the general design shown in post #14 and #18 terminate directly in a 5/8" Baby Pin. I think that these are a possibility, although note that their footprint is smaller than stands that terminate in a Junior receiver, a bit over 1m instead of 1.5m. Female Baby Pins terminating in a 3/8" thread are readily available.
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