April 7 (Eastern Orthodox liturgics) (English Wikipedia)

Rev. Sabine Baring-Gould (M.A.). "S. Hegesippus (about A.D. 180.)." In: The Lives of the Saints. Volume the Fourth: April. London: John C. Nimmo, 1897. p. 110.
The Roman Martyrology. Transl. by the Archbishop of Baltimore. Last Edition, According to the Copy Printed at Rome in 1914. Revised Edition, with the Imprimatur of His Eminence Cardinal Gibbons. Baltimore: John Murphy Company, 1916. p. 98.
Rev. Sabine Baring-Gould (M.A.). "S. Calliopus, M. (A.D. 304.)." In: The Lives of the Saints. Volume the Fourth: April. London: John C. Nimmo, 1897. pp. 110-112.
Very Rev. John O'Hanlon. "Article VI.—St. Brynach, or Brenach, of Carn Engvli, Wales. [Fifth Century.]." In: Lives of the Irish Saints: With Special Festivals, and the Commemorations of Holy Persons. Vol. IV. Dublin, 1875. pp. 75-76.
Rev. Richard Stanton. A Menology of England and Wales, or, Brief Memorials of the Ancient British and English Saints Arranged According to the Calendar, Together with the Martyrs of the 16th and 17th Centuries. London: Burns & Oates, 1892. pp. 146-149.
Very Rev. John O'Hanlon. "Article I.—St. Finan, Patron and Abbot of Kinnetty, King's County. [Sixth and Seventh Centuries]." In: Lives of the Irish Saints: With Special Festivals, and the Commemorations of Holy Persons. Vol. IV. Dublin, 1875. pp. 57-72.

holytrinityorthodox.com

April 20 / April 7. Holy Trinity Russian Orthodox Church (A parish of the Patriarchate of Moscow).

mospat.ru

(in Russian) 7 апреля (ст.ст.) 20 апреля 2013 (нов. ст.) Archived 2014-02-22 at the Wayback Machine. Русская Православная Церковь Отдел внешних церковных связей.

oca.org

Martyr Rufinus the Deacon at Sinope. OCA - Lives of the Saints.
Martyr Calliopius at Pompeiopolis in Cilicia. OCA - Lives of the Saints.
Venerable Serapion of Egypt. OCA - Lives of the Saints.
St George the Confessor the Bishop of Mitylene. OCA - Lives of the Saints.
Venerable Daniel the Abbot of Pereyaslavl-Zalesski. OCA - Lives of the Saints.

orthochristian.com

April 7 / April 20. Orthodox Calendar (pravoslavie.ru).

orthodoxengland.org.uk

April 7. Latin Saints of the Orthodox Patriarchate of Rome.

synaxarion.gr

Great Synaxaristes: (in Greek) Οἱ Ἅγιοι Ρουφίνος καὶ Ἀκυλίνη οἱ Μάρτυρες καὶ οἱ σὺν αὐτοὶς διακόσιοι Μάρτυρες. 7 Απριλίου. Μεγασ Συναξαριστησ.
Great Synaxaristes: (in Greek) Ὁ Ἅγιος Καλλιόπιος ὁ Μάρτυρας. 7 Απριλίου. Μεγασ Συναξαριστησ.
Great Synaxaristes: (in Greek) Ὁ Ἅγιος Γεώργιος ὁ Σημειοφόρος Ἐπίσκοπος Μυτιλήνης. 7 Απριλίου. Μεγασ Συναξαριστησ.
Great Synaxaristes: (in Greek) Οἱ Ἅγιοι Ἐπιφάνιος, Ρουφίνος καὶ Δονάτος οἱ Μάρτυρες καὶ οἱ σὺν αὐτοῖς μαρτυρήσαντες. 7 Απριλίου. Μεγασ Συναξαριστησ.
Great Synaxaristes: (in Greek) Ὁ Ὅσιος Λεύκιος ἐκ Ρωσίας. 7 Απριλίου. Μεγασ Συναξαριστησ.
Great Synaxaristes: (in Greek) Ὁ Ὅσιος Δανιὴλ τοῦ Περεγιασλάβλ. 7 Απριλίου. Μεγασ Συναξαριστησ.
Great Synaxaristes: (in Greek) Ὁ Ὅσιος Γεράσιμος ὁ Βυζάντιος. 7 Απριλίου. Μεγασ Συναξαριστησ.
Great Synaxaristes: (in Greek) Ὁ Ὅσιος Ἀγαπητὸς ὁ Τυφλός. 7 Απριλίου. Μεγασ Συναξαριστησ.
Great Synaxaristes: (in Greek) Ὁ Ὅσιος Σάββας ὁ Νέος ὁ ἐν Καλύμνῳ. 7 Απριλίου. Μεγασ Συναξαριστησ.

web.archive.org

(in Russian) 7 апреля (ст.ст.) 20 апреля 2013 (нов. ст.) Archived 2014-02-22 at the Wayback Machine. Русская Православная Церковь Отдел внешних церковных связей.