Johnston has failed to negotiate Kean's release from Blackburn, where he is currently first-team coach, despite having been hopeful of coming up with a deal that would avoid paying the Premier League club a reported £200,000 in compensation.
With his number one choice now out of the picture, Johnston has begun sifting through other applications, which he claims have come from across the globe.
Indeed, there are reports Germany's World Cup and European Championship-winning midfielder Thomas Hassler has put himself forward for interview, while former Romania boss Victor Piturca is also said to have declared an interest.
Johnston told the Daily Record: "Kean is no longer an option but other names are coming in from all over the world.
"I'm open minded on who we turn to next. Pre-season training begins on July 5 and maybe it's time we went for a fresh approach after years of following a more traditional path.
"I'm not going to exclude anyone on the grounds of geography."
Gus MacPherson, who was sacked by St Mirren last month, has also been heavily linked with his former club.
Johnston said: "Gus was put to us by a third party. He is out of contract and time is against us.
"I'd hoped to be in a position to name a new manager this week but that will be impossible."
Source: Team Talk
Source: Team Talk