Depending on which 4" Grub mold it is it could have been by Chris at Ultra Molds. It should have a model identification on the mold. I have 5 of the 4" Curly Tails that I bought from Dave and Ultra Molds is still producing this mold.
The best that I can remember, back in the day when I bought my tube molds, they were about $65.00 to $85.00 each, depending on the size. Now they are $108.50 to 129.50 ,depending on the size, for the same molds.
I talked to them about a month ago. The site went down and they decided not to put it back up. They are still in business, you can give them a call and they will take your order over the phone.
This is the best way that I have found. Put them in a plastic sandwich bag and vigorously rub them between your hands. This will create static electricity that will cause the strands to seperate.