ASTRA H SRi XP Z18XER
Check online, or google search those lsited above, and you should be redirected to a supplier.
Personally I'd get the Veccy Pipe and remove the pipe in the airbox, new panel filter, and go cat back, but it's your ride
Cybox, Remus, Sportex are all good makes, Cybox is on ebay if you search for them.
Astra Coupe Bertone 1.8
I have the simota on my 1.8.
I have had the Viper, and the VXR intake with panel filterl, and this is the one that makes me smile the most when I drive the car because of the sound