Pole line fasteners are normally manufactured to ASTM A307A, which is a low carbon mild steel, however there are occasions where the question is presented on the availability of high strength graded pole line fasteners. High strength pole line fasteners are not commonly required and would need to be specially manufactured and heat treated to a given specification on a per order basis. An exception would be ASTM A325 heavy hex structural bolts, which are typically available off shelf and would not need to be specially made. This is assuming that the size of A325 required is a standard, off the shelf size.
An example of a common pole line fastener required to be made from a higher strength material would be what are referred to as bent bolts (or bent rods). Although these parts are more commonly made to ASTM A307A, there are times when they are called out as being made from 1045 steel. 1045 is only a raw material however and is not specific to any particular ASTM specification. As a result, they do not need to be heat treated, however they do require a stress reliving process after the bending has been performed. Again, although these parts have been specified as 1045, it is much more common to see them made to ASTM A307A.
As with fasteners in many industries, some are readily available whereas others need to be specially manufactured on a per order basis. This is the case with low strength graded pole line fasteners as well as high strength; however it is much less common for pole line fasteners to be required in high strength grades. If a high strength grade is specified, the bolts would need to be manufactured by a company that not only has the ability to forge, point, thread and galvanize the bolts, but also the ability to heat treat the bolts to the required specification.