Generally speaking you request them from a regional internet registry (RIR). In North America, the RIR is ARIN https://www.arin.net/resources/guide/request. Bear in mind it’s harder and harder to get V4 addresses from an RIR these days, but it’s still possible. Once they are allocated to you, you have to find a place to announce them. Some “cloud” based solutions are Neptune Networks (https://neptunenetworks.org/) or Vultr (https://www.vultr.com/).