How do you convert barcol hardness to shore d hardness?

You don't convert Shore to Barcol or reverse. They aren't directly related, that's why you can't find any references for it. Shore D is a "softness" measure and Barcol is a "hardness" measure.

The best bet is to go to the manufacturer of the product and ask directly for the number you need. They can easily test the material and give you an answer, but convert one to the other...you're asking for trouble.