I'm sure. I have complete every quest in the game, and i have found the required egg into a rare high rank den.Are you sure it's very heavy and not quite heavy? Because those two are very different, quite heavy is lighter than heavy and heavy is the heaviest possible in the editor, so it's not something that should be possible unless you can cause an underflow or something. I only do high rank dens and I haven't found one, only quite heavy and heavy, same for the eggs from the labyrinth... Btw, you may find what you are looking for in the labyrinth, but know that there's no subquest requiring you to have a recipe, but rather find the bead/jewel itself. Many of them can't be combined, only found.
Also,there is a reward for all recipe. I have complete all quest Again, but i dont have all recipe.