Scot Symon won one cap for the football team, against Hungary in 1938, and famously took 5 wickets for 33 runs while bowling against the Australians earlier that year. That match against Australia was at Dundee's Forthill ground on 4-5 August, and he also played in a one-day match at Hamilton Crescent in Glasgow on 6 August, taking 3 for 44.
In an earlier era, John Macdonald (Edinburgh University and Queen's Park) won one cap at football against England in 1886, having already played cricket for Scotland against the Australians in September 1880; he also represented his country against the Gentlemen of Philadelphia in 1884.
Moving to the modern era, Hearts striker Donald Ford played three times for Scotland in 1973-74, twice coming on as a sub for Denis Law and finally making a start against Wales. He was a member of our World Cup squad in West Germany but didn't get a game. A talented cricketer with West Lothian, his only appearance with a Scotland XI was a 40-overs trial match against Worcestershire in 1980, and although he was a member of our B&H Cup squad that year he didn't play.
The trouble with all the above cricket matches is that none of them is formally considered a 'first class' match.
Which brings us to the only football international to have played for Scotland in a first class cricket match. Andy Goram won 43 caps in goal for Scotland between 1985 and 1998, when he famously walked out just before the World Cup. He played five times for Scotland at cricket from 1989 to 1991, and two of those games are considered first class: they were both against Ireland, on 8-10 July 1989 and 22-24 July 1991. By then, he had signed for Rangers and Walter Smith made it clear that he had to hang up his bat and focus on the footie. He was rumoured to be contemplating a comeback with Uddingston CC this summer at the age of 48, so there is life left in the Goalie yet.