Some players buy 10 stock for 11,350 gp and wait for a re-stock to buy another 10, they then go sell at the Grand Exchange for around 3k each. This way is not very recommended to use this way as players can sell to other players for around 5k saying it's very rare to find.
The Frog-leather body can be bought from Reldak in the market place of Dorgesh-Kaan. It can also be looted from the Dorgesh-Kaan average chests, which require 52 Thieving to unlock. This piece of armour requires 25 Defence and Ranged to wear.