Well, lots of box stores, garden centers, etc have no idea if dolomite is in the lime they sell. Also, if your area is abundant in magnesium most likely dolomite is not something that would be stocked in your area.
Sometimes it's best to look at a bag of garden lime and read the ingredients, it may list dolomite there but not on the front of the bag.
No worries. For container tomatoes a bit of "regular" lime will suffice, offering the needed calcium.
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