From the Lobbying Register Team at the Scottish Parliament. The Team is responsible for maintaining the Register and producing lobbying guidance.
From the Electoral Commission. It has a range of guidance on electoral law and non-party campaigners, which includes charities. Each year the Commission publishes specific guidance for elections happening that year.
From a charity law specialist. If you plan to campaign during an election period, you may wish to get independent legal advice. Lawyers specialising in charity law can be found from the Law Society of Scotland.