Be patient...I’ve been scouting eBay, Chrono24 and the m2m rep forums...it takes time. Eg, got a gen DSSD crystal from m2m, including the donor watch, for half the price of the crystal alone on eBay and Chrono24.
Usually you get better luck with Rolex, price is the only issue...other brands are harder/more scarce and much more pricey (Patek or Vacheron).