If you bought the receiver and crystal at the same time, from a hobby shop, they should have told you to get a Hitec crystal.

You should always use receiver crystals that are the same brand as the receiver. There are some 'third party' crystals available that are listed as 100% compatible with specific brand receivers. Performance Devices is one manufacturer who says they make compatible crystals http://www.performancedevices.com
Ordering is through shopatron
http://www.shopatron.com/index/191

They do not really have a good deal on products for Hitec. $7.95
They also charge $7.95 for their Futaba compatible part, which is a good price.