I have some experience working for a Class 1 medical soft good company. I’m not sure if you’re asking about the FDA approval process or “grading” as it relates to taking a development sample in one size and making the size range for the product line. The approval information can be found on the FDA website. FDA approved manufacturers can be sourced or the factory may find it agreeable to pursue an FDA license if your business warrants the time and expense. Depending on your plan, I’d look for vendors already manufacturing medical soft goods with similar construction methods and materials that your design requires. If you or the company is truly new to the process I recommend taking a hit on the cost and sourcing locally to overcome communication and logistics barriers.
If you’re looking at grading your sample, and it’s a brand new design without an antecedent , you might consider sourcing products that are similar in fit and function to use as patterns to develop the range of sizes you’re pursuing. This will cause some back and forth with the factory to finalize the fit and function for each size so plan your schedule accordingly. Hope that helps.