For alisnodgrass---
For 40 years I had a "potato fork",used for ALL digging jobs too, never a spade! It was four-tined, and the tines were a 'flat-triangular' section,(not the square section of 'garden forks'), about 3/4" across the flat. They were made just for lifting potatoes! Broke a tine 7/8 years ago, and cannot find a replacement fork in the UK - tried all the usual shops, and our local agricultural auctions too, but no luck. Try there perhaps?
I saw a few 'flat-tined' forks a couple of years ago in German garden centre - should have bought one, but I now have a s/steel 'garden fork'. It is OK, but the old one fitted my hands better!
Good luck!