We also had a rear spring issue with a different GM car.
We found a lot of options on European OPEL & VAUXHALL forums & sellers (but your car was called the INSIGNIA). It will take some research. And you might wait a few weeks to order for the tariff noise to get sorted.
One note of warning with springs and shocks - Euro versions tend to be significantly stiffer due to high speeds and curvy roads. So even the "mid-line" components might be less comfy than you expect.
You can also look at ebay and amazon (but start at their UK sites as the parts are different). Generally, those are not great sites for most auto parts but they could help here due to all the knock-offs IMHO. I found the shipping from both to be fast and reliable. Sometimes a seller states he will not ship to the US but might change opinion with a quick call.
***Euro OEM part numbers
***Bilstein parts lookup site. This is a bit cumbersome. And they recently changed parts numbers again but it gets you started
web1.carparts-cat.com
***UK forum
Share information on all aspects of maintaining, repairing & servicing the Vauxhall Cavalier, Calibra, Vectra, Insignia, Cascada Signum & Sintra. (Now includes separate Cav Mk2 Forum) ( Includes Opel, Holden, Saturn and GM variants)
www.vauxhallownersnetwork.co.uk
*** Some sellers of aftermarket parts
Buy parts and accessories for your vehicle. 100,000+ car parts from 50+ manufacturers can be shipped on next business day
spareto.com
***There are professional cross-reference sites in europe but I can't remember what they are. Once you identify a GM/Opel/Vauxhall/Bilstein part number, they will help you find other options.
Notes:
- Buick, Opel, and Vauxhall may have different part numbers for the same part.
- Figuring out the "identical" suspension height and stiffness of springs in Europe will be a bit of work.
- GM sold Opel and Vauxhall to Peugeot a few years ago so these parts may be relabled sold OEM under the PSA system.
- UK cars are driven on the other side so that impacts a few parts (e.g. headlights, outside mirrors, etc.)