Here is a Vauxhall parts supplier.
https://www.lmfvauxhall.co.uk/store/home.php
However, you will probably need a diagnostic computer check to confirm where the fault is.
On my 1.6 Astra (53 plate) we had an intermittent loss of a cylinder, with the emissions light coming up on the dashboard.
The diagnostic check showed a fault with the coil pack. This sits above the spark plugs, and connects directly on without the use of old style plug leads.
It was this one, which might be the same for you.
https://www.lmfvauxhall.co.uk/store/product.php?productid=16396&cat=2453&page=1