Need rec for calcium/magnesium source- epsom salt?

Think my plants need a little calcium and magnesium and don't want to buy an expensive bottle of calmag. The symptom I'm getting are the rust brown leaf tips.

Is epsom salt only a magnesium supplement? Isn't Epsom available at most drug and grocery stores?

What store normally carries dolomite lime or some kind of lime that adds calcium?

Is there anything special I need to be aware of when using epsom or lime?

Thanks.

VH