This is a list of companies that offer ship models that are either sold as Coast Guard models or can be easily modified to Coast Guard models.
I do not know if they are all still in business. Please search for them on Google.
Airfix
Amati
Argus
Artisania Latina
BaD Models
Barracuda Boats
Battlefleet
Blue Jacket
Coast Guard Models
Constructo
Corel
Cottage Industries
Dakar
Dumas
Dynamic Models
Figure Head
FM
Gear Precision Models
Glencoe
Hansa
Hartman
Heller
Imai
Iron Shipright
Ironclads
Italeri
ITC
JAC Models
JAG
Lee
Lindberg
Loose Cannon
Loyalhanna
Mamoli
Marine Models
Microglass
Model Shipways
Monogram
Neptun
PT Dockyard
Pyro
Revell Niko
Scale Shipyard
Scherbek
Scientific
Testor
TLAR
Trumpeter
White Ensign
In addition, Gold Medal Models offers photoetch kits to replace molded on railings
In addition, L’Arsenal, Veterans, HR Products and Nautilus offer various weapons to replace molded on parts
In addition, North Star offers 3 dimensional figures