Polk MW6501 drivers
There are several on ebay right now. IF you're using a speaker that uses MW6600 or MW6501 I'd jump on these as they're not too terribly common on the used market. Personally I've never seen so many at one time on ebay.
https://www.ebay.com/itm/333993092091?epid=1651737281&hash=item4dc38a23fb:g:p40AAOSwjz5gldIZ
https://www.ebay.com/itm/203448660998?hash=item2f5e7c3406:g:c14AAOSwYDNgmorE
https://www.ebay.com/itm/324706554138?hash=item4b9a04d11a:g:c3EAAOSw7iFg09IT
https://www.ebay.com/itm/174761996773?epid=1651737281&hash=item28b0a071e5:g:fvgAAOSwMkFglqC1
They is also one lone MW6500
https://www.ebay.com/itm/144089338740?hash=item218c64d374:g:Su0AAOSwD9Rg1kwG
https://www.ebay.com/itm/333993092091?epid=1651737281&hash=item4dc38a23fb:g:p40AAOSwjz5gldIZ
https://www.ebay.com/itm/203448660998?hash=item2f5e7c3406:g:c14AAOSwYDNgmorE
https://www.ebay.com/itm/324706554138?hash=item4b9a04d11a:g:c3EAAOSw7iFg09IT
https://www.ebay.com/itm/174761996773?epid=1651737281&hash=item28b0a071e5:g:fvgAAOSwMkFglqC1
They is also one lone MW6500
https://www.ebay.com/itm/144089338740?hash=item218c64d374:g:Su0AAOSwD9Rg1kwG