The best thing you can do is to have some patience and collect items with the prefix/suffix you want to obtain and wait for a microevent with the bonus, if you want a high level scroll it's better to collect just those with only the suffix/prefix, that's what I did and luckily I got what I want (antonius scroll), that said, there was only one in my server and the one who owned it wanted to sell it for 9 millions , when I got the scroll from the smelter I showed the picture to him and only God knows how I felt at that time.
So basically, if you don't have a need for smelting to repair it's the best time for you to smelt hoping for a scroll, because at a time you won't have a choice but to repair your items especially the weapon, and the smelting will took longer and longer.