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You can always reintroduce some when it gets wet... from companies on the net
If you mulch your soil heavily with whatever organic material you have - at least two inches, more if you have it - the soil will remain moist, and the worms will enjoy dragging the mulch deep underground and improving your clay soil. Plus you'll suppress annual weeds. Try mulching a small area of your plot as an experiment (after a good shower), and check for worms in a few weeks! :)