The last gun show I went had a table with two shoe boxes full of old recoil pads for $3.00 apiece. You could look for a similar deal and hand pick something to cut and grind to fit inside the velcro pad.

You could also try cutting a chunk off of a cushioned floor mat. The kind you put in front of your sink, or you could just pay the freight for a new one.

They are less than $40.