where can I find what kind of ammo is safe for this model?
.32 Colt New Police is the same round as
.32 S&W Long. Colt routinely renamed S&W revolver cartridges to avoid putting their archrival's name on their guns.
.32 S&W Long, also known simply as .32 Long, is not sold by most big-box sporting goods discounters. Many local gun stores carry it but prices can be high. However, it is widely available for reasonable prices by mail order.
Word of Warning #1: I strongly recommend against firing .32ACP (aka .32 Auto or 7.65mm Browning) in this gun. Although .32ACP is the same caliber as .32 S&W Long and the cartridges will usually fit in the cylinder, (a) it operates at slightly higher pressure that may cause damage to the gun, and (b) the undersize case rims may wedge in the chambers when the rounds are struck by the firing pin. This can cause the cases to stick, putting added stress on the revolver's ejector star and potentially bending it.
Word of Warning #2: .32 Colt NP / .32 S&W Long is NOT compatible with
.32 Short Colt or
.32 Long Colt. These rounds use a smaller-diameter case with a heeled outside-lubricated bullet similar to .22LR. These rounds are obsolete, hard to find, and generally quite expensive; however, you never know what you might get if you visit a mom 'n pop gun store with lots of old merchandise and ask for ammo for your ".32 Colt".