After looking online and seeing little about this I read that the Carter Delta inserts would fit. It turns out that these are not a direct fit. The lower supporting lip on the Delta is fully round while the Ridgid has a small tongue sticking into the throat opening. There are 2 options to correct this... You can modify the insert to fit the opening, or you can modify the throat opening to fit the insert. I did the latter... About 5 min with a die grinder and I have a perfect fitting Delta ZCI in my Ridgid BS. I'd rather modify the saw once, than be modifying inserts as long as I own the saw.
Just an FYI for anyone looking for this info and having trouble finding it, as I did this past weekend.
Happy Wood Working!