Billy McKay gave the Cobblers a ninth-minute lead with a close-range header after Andy Holt had stayed cool pick him out with a precise cross.
However, Wes Thomas out-paced Ben Tozer to race onto a long punt three minutes after the break before slipping the ball past Chris Dunn in the home goal to claim a point for the Robins.
Sampson said: "In the first half we were excellent and well worth our lead. In fact we should have been 2-0 or 3-0 up. We scored a good goal but other chances went begging.
"We played Andy Holt in attack as we felt we needed a physical presence up there and he did well to make the goal as well as providing a nuisance value to their defence and holding the ball up well.
"We have had players here on loan and they've done okay but we want someone to come to the club for a long time. We are in the market for a new striker and I think that showed as we missed chances and you need someone to put them away."
Source: PA
Source: PA