Have a look through the Advent offerings on Audiodogs ebay store. Located in Parksville, BC.
Quite recently I had a couple of re-foaming projects and obtained new foams from different suppliers. Neither pair of speakers were common so I was unable to locate any surrounds specifically cited for the speaker models I had. I had to shop by dimensions.
A US supplier provided me surrounds for a pair of Technics speakers but compliance of those surrounds proved to be too low.
The second pair of speakers were branded Yamaha and were acoustic suspension type boxes. I happened upon Audiodog's website and saw a pair of surrounds designated as being for Advent speakers, therefore, acoustic suspension and also therefore, high comp;iance. They were a perfect match dimension wise for the Yamahas I was working on.
I ordered a pair and was delighted with them A perfect fit and perfect compliance.
The vendor recommended to me some Nitrile rubber adhesive he sells. I ordered some but found that it set quite fast which I was not comfortable with. I opted for a less fast setting adhesive which I had on hand from an even earlier re-foaming job.
The Yamahas turned out splendidly and sound marvelous.
If I were to need woofer surrounds again in the future, I will be checking Audiodogs first.