You will find references to manuscripts of potential interest for your research in a number of sources, chiefly:
Beyond your literature review, secondary literature is especially helpful for identifying points of departure for your corpus and method, i.e. a few exemplary manuscripts exhibiting the features of interest to you (be they textual, visual or physical) and approaches to their study.
Bio-bibliographical surveys (see the Bio-bibliographical surveys page on this guide) are especially helpful as you begin a manuscript census of particular works or even of works attributed to a particular author.
Catalogues and handlists (see the Finding catalogues page on this guide) are essential for expanding your corpus regardless of topic, and are especially helpful for identifying manuscripts by historical period and locale (i.e. copied, read, owned, etc. at a particular time and/or in a particular place). Of course specialized catalogues such as those addressing particular painting styles or artists, watermarks, bindings, transmission certificates, hands (i.e. palaeography albums), etc. will also be helpful as both a point of departure and to expand your corpus.
Once you have identified manuscripts of potential interest (or even an entire collection), you should also consider where they are currently kept and how accessible they are.
Feel free to be in touch for advice with navigating catalogues, collections, and description.
World Collections (Al-Furqan Digital Library Portal)
Database drawn from the World Survey of Islamic Manuscripts, allowing browse and search on the collections featured in the Survey.
"In 1989 the Foundation set up a research project to investigate, as comprehensively as possible, the present state of Islamic manuscript collections extant worldwide. Scholars were identified and commissioned to carry out a survey in more than 100 countries. The outcome of this project was the World Survey of Islamic Manuscripts publication...The World Collections area of the Digital Library Portal presents the libraries of the World Survey in geographical context for the user to browse and explore interactively. For example, hovering over a library on the world map provides a quick preview of the library and its holdings."