This is a customer forum. You need to either ring Sky or see if you can order one online. As far as I know Sky will only replace remotes for free if they are still covered by warranty. If not, you'll need to pay. Argos/Amazon are worth a look if you need to pay.
Edit: Info found in this forum:-
1) You can order a replacement from Amazon: https://www.sky.com/help/articles/damaged-or-lost-sky-glass-remote
2) You can order a replacement from Sky under warranty: https://www.sky.com/help/forms/streaming-tv-remote
3) Or you can call Sky Customer Service to order a replacement.
