Once you know what part you need you can then go ahead and buy it. This need not be difficult if you have a computer and Internet connection. There are many spare parts stores online; all you need is the name and model number of the part to order it and it will usually arrive on the doorstep within a few days.
You might be wondering if it is really worthwhile buying online as there is the freight to consider. But don't forget that your bricks and mortar stores also have to pay freight on the parts they get - and they then pass that cost on to you, as well as their other overheads. By buying parts online you can often get steep discounts as online stores do not have to pay staff or rent for a shop front. And often they will give you free freight if the cost of your purchase is over a certain amount.