MOTU 200X Castle Grayskull missileIt seems impossible to find one loose anywhere.
Obviously it's not a Transformers part but since the process can be used for general toy repair, I thought I should make a thread here for general reference.
I have been researching and found this place:
http://aldaxstore.com.au/
I like how they make a mold out of that putty like substance (they have a video). It seems workable for what I am trying to do.