10 MHZ Band-Pass Monolithic Crystal Filter (2-pole)

• 1500 Ohm in/out 
• ​Bandwidth of 8 KHZ (+/- 4000 HZ) @ -3 dB
• Bandwidth of 30 KHZ (+/- 15 KHZ) @ -40 dB
• Pass-band ripple 0.5 dB
• Insertion loss: 2 dB max
• Compact HC-49 11 x 11 x 4.65 mm 

Here is a 10 MHZ band-pass filter (-3dB bandwidth of 8 KHZ) It can be used to filter out  harmonics of square wave oscillators and generators for converting their waveform to sine, for isolation improvement and many other applications.

Think about placing two or more of them in series for further narrowing the bandwidth.