Where do I find replacement summer tyres in with following dimension 225/50R17?

If you need tyres for the dimension 225/50R17, the easiest is to search for 225/50R17 summer tyres, 225/50R17 all-weather tyres or then 225/50R17 winter tyres. A search will generate the alternatives available for those dimensions. Once you have identified suitable candidates you can check if they also performed well in tyre tests performance by motor magazines and their characteristics on EU tyre label. Be aware that the tyre label works best for summer tyres.