Do any english translations exist online for the Buddhavamsa ? I cannot find one.
I do not know about any translations but there is this book called "The Great Chronicles of Buddhas". It's a book only about the different Buddhas and the life of them.
It's a very interesting book with lots of material on them such as daily life, teachings, characteristics etc.
The Wikipedia article lists several translations, of which (at least) the last exists as a PDF online, i.e.
The great chronicle of Buddhas, Volume One, Part Two (PDF) (1st ed.).
Buddhavamsa by most venerable Mingun Sayadaw Bhaddanta Vicittasarabhivamsa. He is best known for his memory skills and his role in the Sixth Buddhist Council. The late Ven. Mahasi Sayadaw was appointed to ask the required questions about the Dhamma to the Ven. Bhadanta Vicittasarabhivamsa, who answered them.