Sometimes conferences have their papers posted on the internet, where they are hidden among other items. Sometimes they are kept on a site even though they are or are to be published. I don’t know what is the status of these papers pr date, but here are several papers on Philo available:
The Hellenistic Moral Philosophy unit of the Society of Biblical Literature had a conference in 2005 in which they focused on Philosophy at the Roots of Christianity.
The following papers are especially relevant to Philo scholars: