Hi Barbara. Not being familiar with the Dove Blending Pen, I did a quick Internet search.
Looks to me like the bottles that say "Dove Blending Medium" are the official Dove brand refill:
Dove Brushes: Dove Blender Technique
The bottles with the gold label, like those sold at Simon Says Stamps, appear to be third party refill:
Dove Blending Medium REFILL at Simon Says STAMP!
If you want to give it a whirl, you might consider making your own. This page has a recipe at the bottom to make 1 oz of refill from water, glycerin & alcohol:
Scrapbooking.com -- Article - The Magic of Blender Pens