If you want to have a go at making the wedges yourself, you might check at JoAnn's Fabric store. I know they carry foam. You cut it to size using an electric knife. I've seen this done on many of the home makeover shows on TV where they replace chair cushions with foam and after they cut it to size, they sew fabric over it using a slipcover method.
It would be cheaper than having foam custom cut for you and if it didn't work, you wouldn't be out much money.