I have just uploaded IPOD: Integrated Party Organization Dataset. This dataset brings together a number of existing datasets, some of which only existed on paper. The data contains expert judgements on several aspects of party organization (Janda, Laver and Hunt, Rohrschneider and Whitefield), raw membership numbers (MAPP project), coding of institutions (e.g. Katz & Mair), and much more. You can find the dataset here.