Is there a reliable on-line source for finding the brerachot for commercially prepared breakfast cereals?
I would suggest a site I stumbled on by mistake: Brochos.
That list from the Star-K is so reliable that the author of the Hebrew sefer וזאת הברכה chose to include that English list as an insert. Just a word of caution, though: As indicated on the bottom of that page, things do change - ingredients change, formulas change, pareve/dairy status change. Make sure to check back periodically.
Also, notice Corn Pops are האדמה in the US only. The formula in Canada is different and they are שהכל.
Another problem with the Star-K list is that it lists Honeycombs as shehakol because the first ingredient is corn meal. The problem is that another main ingredient is oat flour which might not be secondary (since significant mezonos is never tafel) and would therefore make its bracha mezonos. Ask your Rav about any cereal you have a doubt on. No list can take his place.
Shalom, licorice twists need to have flour in order to be licorice twists. Without the flour you would merely have "corn syrup-flavoring-food coloring goop". The flour is what makes it into the candy-noodle that we enjoy. To say that the flour in licorice twists is insignificant is very questionable. When I was younger all the brachos guides said to make a mezonos on them and then relatively recently this shehakol idea, based on what you are saying surfaced and became "popular".
There is a Tosafos in Brachos which says that if the mezonos is just a binder or thickener then it is Tafel (secondary). The point of this is that a binder or thickener is insignificant. Some examples of this are: bread crumbs in meatballs, bread in meatloaf, flour in soup. All of these examples are already a food that people would eat without the enhancement. To stretch this principle of insignificant use of mezonos being tafel to something such as licorice twists (that would just be goop if not for the flour) is a strain on my poor brain.
In Honey Combs, the oats are not just to make the cereal sound more wholesome; they are the third or fourth ingredient! The only possibility as to why the star-k says to make a shehakol is they hold the oat flour is merely being used as a binder, but my impression is that oat flour is a very poor binder! We need to ask the cereal company for what function is it included in the ingredients.