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
In order to find Church Slavonic manuscripts in the Bodleian you will need to consult the Summary Catalogue.
An example of a Church Slavonic manuscript held by the Bodleian Libraries:
Written in Church Slavonic in 1429 at Neamt Monastery by Gavril Uric, the first known Rumanian painter, upon the request of Princess Marina and Prince Alexander the Good, the grandfather of Stephen the Great.
MS Canon Gr.122
Some examples of Church Slavonic early printed books held by the Bodleian libraries:
Bible. Ostrog, 1581.
The first edition of the bible in Slavonic. Printed from funds donated by Prince Konstanty Ostrogski for the Orthodox Church in Volhynia.
Bib. Slav. 1581 c.1
Prvi del Novogo Testamenta, po A. Dalmatinu i S. Istianu stimacen [in Glagolitic characters]. Der erset halb Theil des newen Testaments v Tubingen 1562 (40)
Very few Glagolitic books were printed (only 35 editions before 1600): this is one of four printed at Tübingen in the early 1560s, notable for emanating from a Protestant printing press
As a result of the Oxford Google Project (2004-2009) many 19th century books from the Libraries' collections were digitized including secondary literary 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).