How to get a head count months before my Destination Wedding ?

I wouldn't put anything on the STD, but would instead follow up with them in person (or have your parents, etc. touch base with them.) I was worried about this for our DW, so I sent STDs and got a fairly good estimate through word of mouth.

I am sending out invitations a little earlier than normal and set an early RSVP deadline. (We sent out STDs in October and our wedding is at the end of April. By mid-January, I think most guests already know one way or another if they're planning to attend.) I just don't think I'd ask for a solid commitment 10 months out. Too much can change between now and then... jobs, kids, finances, schedules, etc.

Unfortunately, no. Since you are getting married in October, your invitations should go out no later than late March early April. this gives them time to make arrangements. You can then follow-up with your guests around June.