Oxford libraries have very strong collections of Church Slavonic manuscripts and early printed books. There are two standard bibliographies of Church Slavonic manuscript collections in the UK which can be used for locating these. Printed finding aids are still the best way of searching for Church Slavonic materials.
Cleminson, Ralph [et al.] A union catalogue of Cyrillic manuscripts in British and Irish collections London: School of Slavonic and East European Studies, 1988 Shelfmark: Z791.A1.1988.C6
Cleminson, Ralph [et al.] Cyrillic books printed before 1701 in British and Irish collections London: The British Library, 2000 Shelfmark: SIMM.Z1013.2000.C9
For a union catalogue of all early printed Cyrillic books consult the following work by Evgenii Nemirovskii:
Nemirovskii, Evgenii Gesamtkatalog der Frühdrücke in kyrillischer Schrift Baden-Baden: V. Koerner, 1996-2007Shelfmark: Z1013.1996.N4
As a result of the Oxford Google Project (2004-2009) many 19th century books from the Libraries' collections were digitized including secondary literature on Church Slavonic language and texts. Here are a few examples of some digitized versions of secondary literature including some by the important 19th century Slavonic scholars Vatroslav Jagic (1838-1923) and Josef Dobrowsky (1753-1829).