I was hunting for fresh sour cherries to prepare this one for few years. Then I discovered a package of frozen pie cherries (tart cherries, sour cherries) in a store (yea, I know, should have checked freezer section long ago).
Anyway, now there is no need to wait for fresh ones anymore, since these will work the same good for the kompot, they are a lot cheaper and are much easier to find.
Disclaimer: usually sour cherry kompot is made of fresh sour cherries (if you have access to them by a sane price) with pits in.
Removing pits (or using pitless ones) makes it easier to consume cherries from the kompot (even though I kind of like when pits are in, maybe it reminds me of the sour cherry kompots imported from Bulgaria which we were getting occasionally for winter holidays are kids).