Shadow Plan provides the ability to create such a filter by naming a filtering criteria 'To Do Link Present = "No". It presents all non-linked items, so if a top-level item is your project (not linked), and it has children that are not linked, the filtered list will show the unlinked project and its unlinked children.
Any projects with linked children appear with an expansion arrow (so you know linked children are there), but the linked children are not visible. Unfortunately, there's no way to tell those with no unlinked children when the project has BOTH linked and unlinked children unless you manually number items and look for missing numbers (autonumbering does not work because filtered lists are renumbered).
I have another idea, though - Shadow allows you to highlight items when certain conditions exist, and one highlight setting is for "Items linked to ToDo or DB (includes address and calendar links)". I set it to highlight these linked items in blue (you can use any color), then I visually scan the list to see those projects with no blue (= no linked) children. It's not a clean-looking filter, but it's a good way to flag Projects meeting your criteria in a manner that makes them easily identifiable visually. I seem to remember that Bonsai has a similar highlight feature, but I'm not sure if it offers the 'linked item' option - you'll need to check this out.
Let me know how this turns out...good luck!
- MB