Staightening shanks is a simple easy job,and steaming them is the best way, i use a hot air gun to tweek my shanks
JUst lay the shanks over a boiling pan cover with a cloth and leave them for a 10 mins or so that way you never scotch them
Basically any hot air gun will do you dont need a fancy one .mine has to setting,the heat gun is also useful for shaping horn and works well.
The thing is fan the shank with the hot air gun dont leave it in one spot kepp turning the shank whilst you do it and dont scorch the wood,remember that the heat will have to penatrate into the shank and not just the surface before you try to bend it.
I hate bent shanks and will always straighten them if need be. They are stronger and flex better when under pressure
if you come across a shank with a dogs leg on it dont try to straighten it hardly ever works.(by dogs leg i mean where there has been a branch shooting of the shank and causes a knot,
A lot of people think that a crooked shank gives characture its just taste ,just do it the way you want
If you look in the section maked "home made sticks" in the forum and look for the article "my first stick hawthorn " there are some jigs there i use to straighten shanks with in the meantime this may help article from the book "stickmaking a complete course"