Welcome!  As you discovered, there really isn’t a one size fits all bobbin for sewing machines.  With different manufacturers, there will be a different bobbins.  What you really have to do is find a dealer or sewing machine repair shop that deals with your brand of machine.  Sometimes you can make it easier by going to the manufacturers website.  So if, for example, you have a Bernina sewing machine, go to the Bernina site.  They may have a page where you can put in your zipcode and they’ll tell you where the closest Bernina dealer is.  Then you can try and get your bobbin from them.  If they don’t carry it, they can most likely order it for you.  Or you can call your local sewing machine repair shop and see if they can help you get a bobbin.  Hope that helps.  🙂