Here in the USA 9MHZ crystals are common. I've built many filter using them.
however ladder filter like in KNQ7A and others will cave a center frequency
slightly lower than 9mhz (using rocks that test at 9mhz, my filters are more like
8.997 to 8.9985mhz center frequency.) though for this use that should be ok.
You will have to workout the capacitor values to use for that set of crystals.