This is an early Selectomatic machine built by Brother. it uses normal 15 class bobbins, but I'd get vintage bobbins if possible, new ones the last few years have been really inferior. There are often times machines being parted out on the auction sites and any Brother built machine with a similar stitch length regulator will work.
This is one of those machines that without the manual it's almost impossible to figure out all it's functions. I've had my Selectomatic for a few years and it still gives me fits if I don't use the manual. I happen to have the right manual for your machine so if you pm me with your email addy I'll send it to you.
Cari