I've been able to find most parts on pinballspareparts apart from 15 amp fuses. Regarding the coil sleeves, are they standard for all coil types? I've noticed that there are different sizes but the parts manual doesn't refe

For fuses just try an electrical geek style shop - jaycar is the favourite.

For coil sleeves, if you are buying i person from a local pin shop take an old one in. I've never seen an Atari pin, but have put the same size sleeves into WMS, Bally, Stern amd GTB pins.  It's easy to tell if they are "right", will be a nice sliding fit into the coil, no side to side slop and the will protrude a little - maybe 2mm at each end. The only exceptions I've seen to this are knocker and chime units which seem to have a longer sleeve.

Have a look at this site http://www.pinballmedic.net/coil_chart.html  midway down it talks about sleeves.