I replaced the carpet and underlay in mine and the fittings you are talking about were destroyed in the process of removing them and all I did was fit standard blanking grommets in their place. The carpet shouldn't need any help to stay down anyway.
Go to B&Q, look at the electrical componants section and get a pack of Distbribution Board grommits, they seal properly on both sides rather than just one, plus Halfords are expensive considering what they are.
