Between rank20 and 30 I only received guild marks once, and had to wait till rank30 to buy my first book, though I've heard of people getting enough marks before then. I am currently rank38 and have gotten, on average, 1200 marks total fro
2 leves(usually 800ish and 400ish) each reset since hitting 36. Just got enough to buy my 4th book after the reset last night.
I haven't noticed any real pattern to which give them, and can't say for sure if only silver and gold leves have given them... I do all 20+ local leves out of the 3 cities, which has never been more than 7 total. I've gotten them after failing either one or both of the extra attempts. I have gotten them from clearing nine ivies and emerald moss more than once, though even with 100+ rating, only get 400-600.
I'll try to start recording all info regarding color, rank, rating, etc, from the leves that give marks, though sadly, it seems it is purely random and only increases in frequency as you level.