The U-23's operated from 1955-1976 and played 44 international matches against other U-23 sides, including one abandoned game. But if you mean other than internationals then I'm sure they must have played a few during that time. The one I recall is the match at Hampden on Jan 10th 1972 v the West German Olympic XI. I was one of the 5,903 who bothered to turn up to see Scotland win 1-0 thanks to a Willie Donachie goal.
The teams were:
Scotland U-23: Hewitt (Dundee), J Hansen (Partick), Donachie (Man City), Kelly (Arsenal), Philip (Dundee), Buchan (Aberdeen), Brown (Leicester), Jardine (Rangers), Dalglish (Celtic), Steele (Dundee) - sub McQuade (Partick 65) -, Connolly (St Johnstone)
West German Olympic XI: Bradler (Bochum), Baltes (Fortuna Dusseldorf), Bleidick (Bor M'Gladbach), Mietz (Bor Dortmund), Habermann (Eintracht Braunschweig), Bitz (Kaiserslautern), Halb (Eintracht Frankfurt), Hoeness (Bayern Munich), Wunder (Duisburg), Nickel (Eintracht Frankfurt), Stegmayer (Nuremburg)
As for accessibility it is only recently this site became aware that the Glasgow Herald 1937-1962 was (partially) available online and free. There is a list of online sources here