Numrich Arms Gun Parts Corp. West Hurley NY. is a good place to start
Numrich gun parts
Try e-gunparts.com
Check old Taurus catalogs
By it's model name & serial number.
By model and serial number. Go to proofhouse.com
Try e-gunparts.com
On an older revolver, you are not likely to find a model number, since they did not use model numbers. If you remove the grips, you should find the serial number stamped in the frame under the grips.
Crosman offers a free service to locate repair shops that repair older model Crosman airguns. see the link below.
You will have to call S&W to find out.
You will have to call Rossi to find out.
YOu will have to call Colt to find out.
http://www.gunpartscorp.com/forum/