Your search for in wall sub returned the following:

Passive in-wall subwoofer

IN STOCK

• Passive in-wall subwoofer
• 10" woofer
• frequency response 36-120 Hz
  

In-wall surround speakers

IN STOCK

• frequency response 80-20,000 Hz (±3dB)
• 4-1/2" Kevlar® midrange driver, plus two 1" tweeters placed at a 90° angle
• designed to create spacious sound that doesn't seem tied to the speaker

Passive in-wall subwoofer

LOW STOCK

• Passive in-wall subwoofer
• dual 8" woofers
• frequency response 33-160 Hz

Passive in-floor/in-ceiling subwoofer

LOW STOCK

1 person says 

• Passive in-floor/in-ceiling subwoofer
• 10" woofer
• frequency response 33-120 Hz
  

Passive in-wall subwoofer with matching amplifier

IN STOCK

• passive in-wall subwoofer with dual 8" woofers
• includes separate custom-matched 300-watt amplifier
• frequency response 45-140 Hz

Passive in-wall subwoofer with matching amplifier

IN STOCK

• passive in-wall subwoofer with 10" woofer
• includes custom-matched 500-watt amplifier
• frequency response 36-120 Hz

Passive in-floor/in-ceiling subwoofer with matching amplifier

LOW STOCK

2 people say 

• passive in-floor/in-ceiling subwoofer with 10" woofer
• includes custom-matched 500-watt amplifier
• frequency response 33-120 Hz

Home theater speaker system

IN STOCK

2 people say 

• includes 2 floor-standing front speakers with built-in subwoofers, 2 compact surround speakers, and 1 center channel speaker
• system frequency response 16-30,000 Hz
• 5" x 10" subwoofer with 300-watt amplifier in each front speaker

Pre-build box for Artison RCC-600-SM in-wall subwoofer

LOW STOCK

• pre-construction box for RCC-600-SM in-wall subwoofer
• 15-7/8"W x 48"H x 4"D