Collins is the top scorer in League One this campaign – his goal on Saturday against Rochdale taking him up to 20 for the year.
Harford said: "It's testament to the hard work he puts in on the training ground. We as a football club are absolutely thrilled for James, his work rate, his effort and his commitment, and obviously his goals, he's been rewarded for it and I am absolutely thrilled.
"It's a massive honour for him, it's a massive honour for the football club. It's a big pat on the back to League One and the lower league clubs because there are some good players at this level, it's a testament to James, to how hard he has worked. We are as a football club, the staff, the players, the board, we're absolutely delighted for him.
"His movement in the box is very, very good, he gets across defenders, he's a nuisance. He holds the ball up very well, he has performed very well this year at a higher level than he was playing at last season obviously.
"He's improving and I always say you can improve at any age if you keep working hard and keep doing the right things. He's done that, through hard work on the training ground, he's rewarded.
"He will be the first to thank his team mates, he's that kind of lad. He will be the first to echo the contribution made by the rest of the team. With his movement, his power and his strength in and around the penalty area he is a massive threat.
"Robbie Keane called me up the day before the Wycombe game, we had a chat about him and I told him his strengths and Mick called me up the day before we played Rochdale and we had a very similar chat.
"I just told them about James, what his character is like, what he's like as a player, what he's like around the training ground. It was a glowing reference, that's the type of bloke he is. He's a credit to himself in terms of the footballer he is. He works his socks off everyday and he is deserving of his call up.
"James is thrilled, we had a hug and we both had a tear in our eye and it's a massive honour to be called up for your country, he's absolutely thrilled with it. We're delighted for him."
