You will be able to find Short Boost Assists, for free, in the wild. But their main reason to be is to consume your Glow. So if you can spare a fair bit of Glow, you can get a Long Boost Assist. Or many. Up to 6 atm. They're a bit expensive and probably not a good idea to get early on. But once you're all leveled up, and don't need Glow for anything else, call in your assistants! : ]