They are very rare at shops. You will get the most from breaking down all bullets.
9mm and 357 give small pistol primer,
44 and 10mm are large pistol.
308 and 45-70 large rifle.
50mg is its own primer.
5.56 and 5mm are small rifle.
Both shot gun shells are same primer.
22's are just powder and lead.
You can only break down rounds and slugs, no special ammo.