This might work.
Frame your question like this, “Do any of you have any information about such and such?”
Then, after the first person responds, you can make another post that says, if anyone feels like PM’ing me about such and such, that would be great too.
That way, you’ll still get real responses on the actual thread, but people will know that you are also interested in talking about the subject privately.
You can also add into your post (not the Q itself) that you would appreciate it if we could send this Q to any other Jellies who are known to have this type of information (because you might not know). They don’t need to post the names of the Jellies, you would just be asking us to forward your Q to a Jelly who has expertise with the issue.
I’ve seen that done in the past, many times.