Jaime, I think you will really like your 99-13. I also have a 1928 99-13 and they are so quiet. You can get the bobbins for it from sew-classic. Sew-classic also has the manual for the 99 that you can download for free:
www.sew-classic.com/uploads/99K.pdf
The low shank attachments for your machine are quite easy to come by. I have gotten some at flea markets and antique stores. Your local sewing machine repairman might have some too. Good luck with your machine. Don't use anything harsh on her cleaning her up. Sewing machine oil on a cotton ball works great!