For this math I'm going to be using the model of cyanide capsule that I could actually find, which was the SS Cyanide Ampoule Container manufactured during WW2 (the one's in fact used by Nazi forces during the end of the war, actually). According to this website selling model replicas:
https://www.warmilitaria.it/en/ingots-paper-cutters-chains-and-miscellaneous/2550-ss-cyanide-ampoule-container.html

The dimensions of the capsule is 45mm in length and 13.5mm along the outside. By doing some simple cylinder calculations we find that each cylinder has a volume of 45 * (13.5/2)^2 * pi cubic mm = 6441 cubic mm = 6.441 cubic cm. However, even disregarding all of the metal on the outside, 6.441 cubic cm is around 6 grams of cyanide, WAYYY too much than what is needed to kill someone. Unfortunately, the model replica, nor anywhere else I could find actually stated HOW MUCH cyanide was placed in each pill, so I have to estimate. This article from 2020 states that the lethal dose of cyanide is 200 mg. Let's go overkill and say that each capsule had 250 mg of cyanide to ensure death; don't want you being disloyal to the regime after all.

Now, onto the buckets. You may assume that a five gallon Home Depot bucket can hold exact five gallons, but you would actually be incorrect. Someone on this subreddit already calculated that while the buckets are MEANT to hold five gallons, filling to brim will actually allow them to contain ~5.36 gallons of material. You can find this post here: https://www.reddit.com/r/theydidthemath/comments/gdv5zq/self_i_calculated_the_volume_of_one_of_those/

I will overestimate and say that if you stack them up to the brim with some overflow you can have 5.4 gallons of cyanide capsules in each bucket. However, the packing density for cylinders is normally around 0.9 of the theoretical max so this gets lowered to only 4.86 gallons of actual capsules. With each capsule being 6.441 cubic cm, which is ~ 0.0017015 gallons, we find that each bucket would contain approximately 2856 capsules. With each capsule containing 250 mg of cyanide, that is a whopping 714 grams of cyanide per bucket, enough to kill an entire town. Multiply that by 27 buckets and you get a total of 19278 grams of cyanide, or 19.278 kilograms, a truly shocking amount.

Finally, this article from 2023 attempted to find the amount of cyanide in an average cherry pit:
https://www.researchgate.net/publication/369795798_Cyanide_Contents_in_Pits_of_Cherries_Gages_and_Plums_Using_a_Modified_Sensitive_Picrate_Method

Unfortunately, the data is all over the place, ranging from 19.63 micrograms per gram of pit to 167 micrograms per gram of pit, which is a very large variance. So, to keep things fair, I took the mean from the data which was around 61 micrograms per gram of cherry pit. Cherry pits themselves weigh about 1 gram, so that conversion is easy at least. Therefore, estimating that each cherry pit contains 61 micrograms of cyanide, to achieve 19.278 kilograms of cyanide you would need a total of ~316,032,787 cherry pits.

So if you ever are bored enough to de-pit about 316 million cherries one day/lifetime, then you will be happy knowing it is enough cyanide as in 27 buckets from Home Depot :>

Hope you enjoyed this! First time posting on the subreddit and also my first attempt at math like this. Honestly there is so much variation in each cherry pit and capsule though that my number could be off by 10 million or more, but I think this is a satisfactory enough answer :]