I am sure the club may have sills in stock to sell to its paid up members, alternatively as listed above and found elsewhere on tinterweb sills are available... Its about the one and only part that's still made
Yeah the sills are widely available from any auto factors but the prices seem to have gone up a fair bit lately and I'm sure there is a good saving to had buying from the club.
If your a non member then the saving you'll make buying the club ones would almost cover the membership fee!