Polk Audio Atrium 4 Woofer 4.5" RD4528-1 - Speaker Exchange
Polk Audio db651s 6-1/2" 2-way shallow-mount car speakers at Crutchfield
Polk Audio PSW505 Replacement Woofer RD5055-3 | eBay
Amazon.com: Polk Audio PSW505 12" Powered Subwoofer - Deep Bass Impact & Distortion-Free Sound, Up to 460 Watts, Easy Integration with Home Theater Systems, BLACK : Electronics
MW Audio MW-8000: 8 inch Polk Audio Copy Woofer | Midwest Speaker Repair