A while back I was replacing the 10.240 a lot on 360014 boards and lately, more than just one here or there on the 15s and the 6900s. The spec sheet on CB Tricks has the 10.240 HC 49 U at 20 ppm with a load capacitance between 15-50p (Specialtel-Lem who are no longer in business). I found two places selling them (EYCAB10240) for 4 bucks BUT they hammer you with 10 for shipping whether you buy 1 or 10 (now the cheap old guy comes out in me).
Much larger distributors are...
10.240 crystals and a Cheap Old Guy.
Much larger distributors are...
10.240 crystals and a Cheap Old Guy.