I see that Unicode has both upper- and lowercase digamma (0x03dc and 0x03dd), as well as qoppa (0x03dec and 0x03df) and sampi (0x03e0 and 0x03e1). I'll try pasting them in as XML entities, but that might not work: Ϝ, ϝ, Ϟ, ϟ, Ϡ, ϡ. (I only see the capital versions in my browser.)

The URL below has the PDF for this section of Unicode and includes Coptic letters, too.