.32 S&W Long
If that doesn't work you will need to compare the serial number and figure out the manufacturing year, there were minor variations depending on which decade it was made; and of course there are a handful with aftermarket modifications. But the 'police CTG' models should have no trouble using .32 S&W Long.
It should also be interchangeable with other ammo of the same size such as:
.32 Colt New Police
.32 Colt Police Positive
Size
38 caliber revolver ammo
A Colt police positive ,32 with that serial number was made in 1909.As far as ammo,you can check with any gun shop.
Have it checked out by a good gunsmith.
A Colt police positive .32 with that serial number was made in 1916.
.38 special Stay away from the "+P" ammo
yes, plenty of ammo available.............
Gun shops, gun shows, on line, pawn shop,
100-1000 USD
You need a good gunsmith.
about 1910
made about 1913......