A UPC/EAN barcode is a simple graphical representation of a 12-digit (base-10) code plus check-digit. Any such monochrome vector graphic can easily be represented by a glyph, or sequence of glyphs, in a font. You just need a suitable algorithm to calculate the necessary character code sequence in your chosen barcode font to represent your UPC code, which will begin and end with the characters representing the guards. These are commonly available as spreadsheet macros but might need careful reverse-engineering to make a Panorama function.
It’s the 13-digit number that is unique and subject to a one-off or annual payment. Anyone can make a graphical barcode from a UPC code (e.g. the ISBN of a book), whether or not it belongs to them, either by copying the number into an online barcode generator and downloading the resulting EPS/PDF/TIFF/PNG graphic or, if it’s necessary to automate the process, using a barcode font in conjunction with the appropriate character-encoding function, or by assembling rectangles of different sizes in the correct order as you have been doing.