License a company prefix from GS1 US. This is a variable length number based on the number of unique SKUs you need to barcode.
Use GS1 US Data Hub to create and manage UPCs. This is a free account for single user accounts but there is a fee to purchase your company prefix -- pricing schedule is provided below.
Place barcodes on your products. This can be done gradually since you'll likely want to incorporate it in your packaging process.