I'm not able to reach Professor Reynolds directly and none of the authors of the papers that have used his scale have replied to my emails. If anyone has used this scale then please let me know if I can use it with relevant citation. Thank you
The best way to obtain permission to use an academic instrument or scale developed by someone else is to locate the copyright owner or publisher. Since you have not been able to reach Professor Reynolds directly, you could attempt to reach out to the publisher of any articles that have cited the scale. If the scale is copyrighted, you may need to obtain permission from the copyright holder to use it.
It's also important to make sure you follow any guidelines or requirements specified by the copyright holder or publisher, such as providing proper attribution or paying a licensing fee. If you are unable to locate the copyright holder or publisher, you may want to consult with a copyright or intellectual property lawyer to explore your options.
It's crucial to obtain permission to use the scale, as failure to do so could potentially result in legal action for copyright infringement. If you are unable to get permission, it may be necessary to find an alternative scale or develop your own.
Article Measurement of Academic Self-Concept in College Students
(follow the DOI), you need to request from them, as Ajit Singh already wrote. On the site of the original article you find the point "requests and permissions" under which you probably will select the "academic permission". That will redirect you to Rightslink which is the standard tool used by almost all big publishers for such occasions.