Mustchin's form brought him to the attention of Scotland coach Frank Hadden - now assisted by Edinburgh head coach Robinson - and with Scotland's regular second-row forwards in short supply, Mustchin was handed a call-up for the tour to Argentina.
The Edinburgh pack star partnered Scott MacLeod in the engine room as Scotland returned home with a 1-1 draw in the series against the side which finished third in last year's World Cup.
Now Mustchin has his sights set on maintaining his place in the squad for the Autumn internationals and beyond that the 2009 RBS 6 Nations.
It is one of the most competitive areas of the Scotland scene with MacLeod, Jim Hamilton, Scott Murray, Ally Kellock and Nathan Hines all vying for a place.
But Mustchin said: "The last nine months have been like a dream come true for me. Seeing Edinburgh achieve our best ever finish in the Celtic League followed by earning caps for Scotland was unbelievably good.
"I can't wait to return for the new season; it should be even more exciting than the last one," added the line-out specialist.