Try Numrich www. gunpartscorp.com
That is also known as .25ACP, most gun shops carry it.
Brownells gunsmith and Down East guns are two places to find parts for the pistol. You can also find parts at auction shops and local gun stores.
go on the computer and scan the words 'marksman air pistol' ...............
Try e-gunparts.com
Try e-gunparts.com
try the gunpartscorp.com
Try e-gunparts.com
Try e-gunparts.com
check on line for CVS gun parts
GUNPARTSCORP.com and JACKFIRSTGUN.com carry lots of parts.
Try Numrich Gun Parts at the related link.
numrich has parts for all kind of guns, including Colt's.