If you can wait till out next bulk purchase, CO&W Co could get you a 4" for about £20, (ex VAT ex Handle) or you could buy mail order from Woodcraft In the US or try myoldtool.com in Texas for old ones
Froes can be had from Bristol Design,
Magard Ventures (Canada) or Axminster Power Tools.

Bill

The pessimist sees difficulty in every opportunity

While

The Optimist sees Opportunity in every difficulty