In the past I have used website that can generate barcode images, and I manual insert these into my page layout software which I then print to label sheets. It's a manual process, but I started with the Square POS that didn't generate barcodes. Once you have a system in place, it can go pretty quickly to edit/make new ones.
I purchase labels from Onlinelabels.com. They have different sizes, but I use the letter size and layout multiple labels on one sheet. and what it really nice is they stick to my retail store items, but they are still easy to remove. They also have online tools to help print barcodes.
Hint: I don't have a dedicated label printer, just a standard letter-sized printer. I found the printer can make a difference in how small I can make a barcode; my laser printer can print finer lines, so the barcode can be smaller. My inkjet spreads the ink more so tiny lines bleed together. You can also adjust how many characters are in the barcode itself; longer characters make a larger barcode, so if you can shorten or used "codes" to differentiate your items it may work better for you.
Good luck, I know it's the details in business that often create huge roadblocks, but I hope you're able to figure out a solution.
