Is it realistic to get the event CE from as a quest drop?

It depends on your luck. I got 2, but I got more heart than CE or EXP card

It's supposedly a 1.6% Expert / 2% Goddess chance. So *on average*, once per 63 or 50 runs. That said, with that low of a chance, the probability curve is quite flat, so there's still only an 80% chance of getting one by 80 runs

I've been farming expert nonstop and i dropped 5 copies, definitely doable.

I used around 15 golden apples so i didn't even farm that hard.

I got one drop off the expert node, haven't used a single apple. RNG can be horrible or your best friend sometimes.

I already got 2, each one from expert and goddess.
If you say about probabilty, i think its quite possible (at least one :v)

Some events you get 3 to drop with little effort, even on the easy quests with reduced drop rates. Sometimes you spend apple after apple and never get the drop (which really sucks on events with only 4 in the shop)

If you really want to mlb it, start farming goddess as if you are going to buy it, and if it drops before 5k, great and you can buy qp with the dango you farmed if you already cleared the shop.

I got my fifth copy from a drop off the expert node when I was farming for the 5000 dumplings copy. Though, I don't need more than five, so I started clearing the shop by then.

It's all luck, so I wouldn't try to drop it. Just farm as much as you can and maybe you get lucky as well.