Most referees purchase from The RefStop, they are run by referees and understand and tailor to referees’ needs. They are usually also the first to release new gear such as the training wear each season. However, they can be quite pricey, so some buy from sites like Newitts and Kitlocker who are much cheaper - but this comes without the option to add county badges so you may have to DIY with iron-on county/FA match official patches if that is what you are looking to do. There are many other sites as well such as A&H and Refstore but I would say A&H isn’t as popular as it used to be and is expensive and Refstore are Scotland-based so don’t offer many Nike products. You always have the option to purchase via the official county/FA referees store. Have a dig around and you should be able to find some bundles on certain websites to maximise savings, as stuff is expensive!