I don't know if or how many 120 fishing scrolls have dropped on other shards, but a player over at the german forum reported a drop of a 120 fishing on DF. So, yeah, they do actually exist.
here's the link to the screenshot:
http://uob.zarum.de/forum/attachment.php?attachmentid=23241&d=1290463091
What really surprised me, from what I seem to understand, is that the 120 scroll was actually obtained "skipping" the 115 skill level step.
It was obtained while being at 110 skill.
From what I seen to understand, it was a 6-parts order. It would be interesting to know whether there were dungeon fish involved and how many types (just 1 type or more ?) and also, whether all 6 types were requested in 20 quantity.
We know that dungeon fish has the highest weight (1.5 versus 1.0 and 0.5) so, it would be interesting to know whether all quantities were 20 and whether one or more types of dungeon fish where requested to try figure out whether, in order to get a 120 scroll, the order has to be a maxed out one or it can also be something less.
Since I recall reading that at least one type was for 20 lobsters or crabs which has the lowest weight, I would imagine it was not a maxed out order but without more informations it is hard to say.