Speaker cover, felt.

Hi all, my car came with some rubbish 6x9's, which I switched for my vibe ones. The previous owner did a bit of a hack job so I want to go about covering the whole shelf in felt to cover up the choppy cut out and for security purposes. So what and where is a good place to get some back felt that will match the current parcel shelf and won't muffle the sound to badly? Also what attachment options do I have? if there and spray on glue I can use or will I have to tack it underneath?