The current list is used by a range of companies including The Scottish Government and Parliament, VisitScotland and Health Scotland.
Scottish Government deputy director of marketing and new media Roger Williams said another 24 organisations were expected to join the list in September.
The new additions include Scottish National Heritage, the Crofters Commission and Registers of Scotland.
'Hardly any of the new organisations have used PR in the past and may consider doing so now they have access to the list,' said Williams.
The PR roster is being overhauled as part of a statutory review of the Scottish Government's creative agencies.
Barkers, The Big Partnership, IAS Smarts and Consolidated are the PR agencies on the current roster. The current four-year contract expires in July and the new roster will start in September.
Scottish agency 3x1 director Cameron Grant said: 'Without doubt this is one of the most exciting opportunities for PR consultancies in what is the biggest pitch in Scottish marketing.
'PR has been highlighted as a sector that has worked particularly well in the past and hopefully its role will continue to deliver across the many government campaigns that will form part of the new contract.'