AMO is now ATA, but I don't think much changed--string specs didn't. Again though, not all (nowhere near all) bows follow AMO/ATA manufacturing specs. ATA is the Archery Trade Association--changed from AMO a few years ago.
There's a few custom string makers around--not hard to find one at all. Most will make a string for your specific bow. Most suppliers stock "one size fits all" strings, and don't offer different strand counts, different serving sizes (to fit your particular nock), lengths are by the inch or two inches (i.e., your choices might be 55", 56", 57"; or 54", 56", 58") where custom makers will generally make the string the length you say. A good custom string is pre-stretched, offered in different materials, and your choice of colors, 2 or 3 bundles (flemish), etc.