The Ayrshire side confirmed the signing of full-back Sean Clohessy on a two-year deal ahead of the game but the former Arsenal youth player was not registered in time for the match at Rugby Park.
Johnston wants even more competition for places and is keen to bolster his numbers further in the coming days but, for now, was delighted with the capture of Clohessy.
He said: "We missed the deadline by a minute seemingly so he wasn't available. But it will give us good competition for places.
"Young Mark O'Hara did extremely well at right back so he is going to play a big part for us this season as well.
"Hopefully this week we will be bringing in at least another two or three players who will hopefully strengthen us again. That's the plan anyway."
The goalless stalemate with Saints proved to be a largely drab affair but Johnston felt Killie were unfortunate not to take all three points.
He said: "I thought we created enough chances to win the game. We restricted them to very few chances, which was good.
"We were a lot more compact this week compared to last week so there was a big improvement."
Killie could have had a penalty when a William Gros shot appeared to strike the hand of Frazer Wright but there was no spot kick from referee Willie Collum.
Johnston added: "From my position, it looked as though it was a clear handball.
"His arm was outstretched and I think that's an unnatural position, you're not allowed to do that. As far as I know it looked a penalty, but it's a hard decision for a referee in a split second.
"That's where you are maybe looking for your linesman to help you out. You need to make sure you get decisions like that right."