I'm just wondering if I can buy just front wheels? And where can I do that?
Well, there's no store offering that. YOu will have to contact the seller of your pram and/or the manufacturer, Bergsteiger, directly. They should offer you the fitting wheels as a spare part (it might be there's going to be a fee to pay, or as a part of the warranty, they should provide new for free).
Find any retailer of the brand around you and ask for help, or try the Bergsteiger support website.