There are several companies that make fiberglass hulls and resin fittings for various USCG cutters and boats. Lots of scratchbuilding is required.
Wooden USCG boat kits available: Dumas Products has the 44 foot Motor Lifeboat, 41 foot and 40 foot Utility boats; Midwest sells the 47 foot Motor Lifeboat.
Fiberglass hulls and plans are available from:
Scale Shipyard in 1:96 scale: Polar class icebreaker (50" long); Hamilton class 378' WHEC (47"); Bear class 270' WMEC (33"); Cherokee class 205' WMEC (ex USN ATF) (26"). SSY also has the 205' WMEC in 1:48 scale (51").
Micro Glass has the following in 1:32 scale: 95' Patrol Boat; 82' Patrol Boat; 47' Motor Lifeboat; 44' Motor Lifeboat; 40' Utility Boat; 25' Motor Surfboat (lifeboat for WMEC/WHEC). They also produce the 44' MLB in 1:16 scale.
Coast Guard Models has several cutter and boat hulls available in several different scales.