You have the best chance of finding authentic Indian arrowheads by searching ancient Indian campsites. If you are not sure where you can find ancient Indian campsites, you should consult archaeologists, archaeological museums or archaeological magazines that specialize in the area that you are planning to search. Some people have been known to search for ancient Indian campsites by using signs such as burned rock middens, particularly at hill bases with excellent access to potable water in ancient times.
You can also find authentic Indian arrowheads in places where ancient Indians might have lost their arrows. This has uncertain chances of success, but if you find a stone with what looks like ripple marks on its surface, you might have found something that was man-made. The greater the number of ripple marks, the smaller the chance that those flakes were chipped away by natural processes.
If you are not sure where to start, you should check creeks in your area because erosion can sweep authentic Indian arrowheads as well as other items of interest into their waters. Generally speaking, you can find said items either close to the headwaters or in quieter stretches of the creek where sizable objects have the chance to settle.