My early 642 came with the Uncle Mike's grips. It is my understanding that those grips were discontinued because of a licensing disagreement between Uncle Mike's and Craig Spegel, the designer.
I don't know that there is a replacement that is similar. I know that some replacements interfere with speedloader use (the Uncle Mike's do not). One possible solution is to have Craig make a set for you out of wood (I like Cocobolo and Kingwood). They won't be cheap, and delivery times are a bit long, but none of that will matter when you finally get them.
Here's a set of Craig's Boot Grips+ in Cocobolo on one of my 625's. They're about ½" longer than standard boot grips, but you can see what his work looks like.
Buck