I have found a German firm which offers Rigby style M98 fully inletted and finished stocks, https://schaftwerk.de/. I found the prices to be reasonable, the delivery time as well and the shipment cost from Germany, at least to the US, is reasonable, too. An example of their design can be found here: https://www.egun.de/market/item.php?id=7141056

Edit: Fixed URL reference.