Rovers are currently operating under a transfer embargo after failing to meet the Football League’s Fair Play requirement.
Blackburn, Leeds and Nottingham Forest were all punished by the Football League in December, and Johnson concedes the situation has presented challenges.
Johnson said: “Basically we can only sign free transfers and loans because of the Financial Fair Play which has been incurred in the last six months.
“So, it’s really difficult. We can have a maximum 24 players as well and there are constraints on the salaries.
“Everyone knows what Blackburn is like, the facilities etc, so it’s not a problem getting to speak to the players and to show them what we have got here. All the facilities are excellent.
“It is difficult with the wage constraints, but we have been in it now for a few months and we know the cards that we’ve been dealt. It is difficult but there are players out there and we’re making inroads with a few at the minute.
“We can sell players, and who knows if we get enough bids for some of our players who might go in the window, but we can’t go out and spend the money, that’s the difficult thing. That goes to probably paying off the fine that we would have to pay to get out of the transfer embargo.
“But as I said, we know what we’ve been dealt with, and it’s just a case of looking around, using our contacts and trying to get the players in to enhance the squad.”
And the former Derby, Aston Villa and Celtic striker is working round the clock with Rovers manager Gary Bowyer to identify new players as they look to strengthen before the Championship campaign resumes in August.
Johnson said: “All the time. We’re on the phone 24-7 most days of the week, and probably until the window finishes, and then we’ll see where we go by the end of August.
“We’ve got the nucleus of a good squad and we just want to try and carry it further now. Some of the lads have renewed their contracts, probably been offered better contracts elsewhere, but it just shows the stature of the club.”