Can a druid select Improved Natural Attack as a feat? Please support your claim.
There is no rules support for it. You can try to say you leveled up while you were in a form that qualified, but that is still up to the GM to determine if you need permanent or temporary access to an ability unless otherwise stated.
So to prove that the rules allow it or do not allow you it someone would need to prove how much access is needed to qualify. There are no rules which address this with regard to this question. The only situation that calls out much access is needed for anything similar is taking ranks in the fly spell, but that is specific to that situation. It doesn't address this one.
By level 8 a druid can be in Wild Shape 24 hours a day - that's effectively permanent access a natural attack.
RAW: Monster feats are available at GM discretion.
By level 8 a druid can be in Wild Shape 24 hours a day - that's effectively permanent access a natural attack.
Thats still not permanent and if someone is being really strict a work around still won't count if it is exactly what is needed.
Technically, I believe by RAW they can, if you take the nature fang archetype and use your slayer talent to pick the natural weapon ranger combat style, but something tells me you want it for wildshape... In which case the only way I know is GM discretion :)
Take the Adopted trait for half-orc and get a bite attack. (Or actually be a half-orc with Tusked or Toothy.) Hard to argue that's not a permanent natural attack.
Which would only work if you wanted Improved Natural Attack (Bite). If you wanted Improved Natural Attack (Claws) (or any other natural weapon type), you are still out of luck. Because the feat requires you to choose one of your natural attack forms - if you don't have that natural attack form at the time, you can't choose it.
My personal opinion - it would work like the Fly skill.
You cannot take ranks in this skill without a natural means of flight or gliding. Creatures can also take ranks in Fly if they possess a reliable means of flying every day (either through a spell or other special ability).
As long as you have a "reliable means of X every day". Wildshape would be such a means (it certainly is for the Fly skill. Again, however, my personal opinion. By RAW, you must have the natural attack at the time you choose the feat.