Not quite sure about on-line courses, but I'm sure you could do a search on Google - or whatever for one.
I can reccommend the BBC interactive course though, think it's called "Get into Greek" available from WHS, or ebay (etc) I used this one - in the days before interactive - along with a course at my local college & that, combined with 2 years in Cyprus set me up for the (quite complex) basis for continuing !!
That was more than 10 years ago, but it must've been good, because I still have a fairly good recall of most of it !
"an thelis - tha mathis" !
I could've written it in Greek, but too much hassle to get the Greek symbols up on here !