The easiest way is to make a batch of 2 (or more) supplement. One of the items will need to be a Royal Crown to give you Royal Style, the other item will need to be a high level item like a another Royal Crown, Gomphrena, Azure Wing, Forest Dew etc with the trait Enhanced so that you have enough cost to put Royal Style on the final supplement.
Try spamming tonics at the gather point for these types of items until you get lucky.
Or you could use the Royal Crown that Astrid stole from you which has Enhanced on it.
i have supplements with royal style, but the trait can't go on ingots, and i can't find a way to put it on a synth/dev category item to get it on the accessory. it'd be so much easier you could use a royal crown in the actual synthesis of the accessory
also, how do you get null ailments trait on an angel charm? it only seems that regentiums just barely make the mark, but i need to use blessed coins on the charm...although i'd really like to have that trait. which ingot can raise that bar high enough for me to use a blessed coin, and to get the trait?
I used a max quality Heat Proof Plate to make the mark for the null ailments effect and carry some of the traits. You can also very easily get a max cost pure oil into a HP plate wihich can help with several stages of synthesis.
Bless Coins and Ultimate Steels can be used to make HP Plate so you can just transfer the traits over. I'm not sure about the coin, but Ultimate Steels can definitely take supplements at various stages.