Hi, your best bet is www.espncricinfo.com
Search for counties, Northants, results then archive. This should give details of every match played in the club's history.
If you search for David sales cricket archive, it will bring up his page. Scroll till you see lists of matches and detailed statistics. Use this link and then scroll to "first class matches played by David sales"and it lists all his matches. The 2 you want are 24th July 1996 and 30th July 1999 v Essex
With your help l have now located those scorecards.
Can anyone tell me on which ground did David Sales score 70* as a sixteen year old? I was there but it was a long time ago and l can't remember where the match was played. I think it was a one-day game.