Grand Master Medic

To learn the skill you need 350 skill in first aid. It allows you to aquire skill until 450. When you skill up to 390, Manual: Heavy Frostweave Bandage can be acquired. It is a world drop so dont worry about farming for it. Doing any instance will propably wield it for you.

Frostweave Bandage trainers listed below.

For Alliance:

Anchorite Yazmina - Valgarde Keep (Howling Fjord) -- Found at the Bonfire, near the dock. --
Brynna Wilson - Valiance Keep (Borean Tundra) -- Found next to the Blacksmith Trainer, near the Sparring Footmen and a very interesting and curious "thing". --

For Horde:

Sally Tompkins - Vengeance Landing (Howling Fjord) -- Found on the top floor of the Building, next to the Flight Master. --
Nurse Applewood - Warsong Hold (Borean Tundra) -- Found behind the stairs below the Zepelin landing platform, near the trainers for enchanting/tailoring. --

For Both Factions:

Olisarra the Kind - Dalaran (The capital city of Northrend) -- Found in the Magus Commerce Exchange area of the city. --

~ Politsos -- EU - Haomarush --

Grand Master First Aid Trainer, Brynna Wilson, is located at 57.8, 66.4 in Valiance Keep. This is the first town you enter when arriving by boat to Northrend.

She will increase your potential First aid skill to 450 (for 50g) and teach you Frostweave Bandage (for 8g).

It's WotLK.