All plants require calcium as it is used in the construction of cell walls. Any decent orchid fertilizer should contain it as calcium is one of the macronutrients required for plant growth. If you are still concerned, calcium nitrate can be purchased and applied at a rate of about a half teaspoon per gallon of water. Any deficiency would first be noticed on Cattley type orchids in the warm growing season. Look for brown leaf tips and yellow bands around the pbulbs.
Jim
