I have never seen this term used exclusively to be honest. In many traditions the four elements are corresponded with the four cardinal directions of a compass; East, South, West, and North.
These elements are given various faces and forms from tradition to tradition. You of course have the spirits used in early hermeticism Sylphs, Salamanders, Undines, and Gnomes. The reference to working with them which comes to mind is Eliphas Levi's book Transcendental Magic. The extract which I am thinking of can be found here-
You also have the watchtowers of the elements, which were orginated in the Enochian system of John Dee, Adopted by the Hermetic Order of the Golden Dawn, and then made a practice in Gardner's Wicca. In my opinon they refer to the Enochian angels of the respective Enochian tablet- of which there are four united by a tablet of Union which represents 'spirit'.
And my last example would be the most famous one as developed by the Hermetic Order of the Golden Dawn in their pentagram ritual. In this ritual the elemental personifications/guardians are represented by the Archangels; Raphael, Michael, Gabriel, and Uriel.
I am afraid those are the only ones I can think of off the top of my head, if you had a particular tradition in mind, it may be useful to list it and someone else may be able to give you a more informed answer.
Is there anywhere I can go to directly study this form of Elemental Guardian because I've been studying for a long time even before the first post but I always feel like there something missing from everything I've learnt
Not exactly what i'm looking for i'm looking for information on elemental guardians in a sense of aspectual guardians from what I know there are some for every aspect of life from emotions to historical events and they can be bonded with in a spiritual sense on a spiritual level