We went to the new parents evening at DS's school (not BGS). We were given a pack containing useful info - like uniform, stationery requirements, booking form for music lessons etc. The HM's speech was not significantly different from the open evening when we went round before choosing schools apart from the boys were addressed as members of the school rather than prospective pupils. There was a chance to meet the head of Y7 but imagine trying to do that with 150 other parents and boys
so we didn't bother. There were also representatives from the PTA looking for new volunteers.
I would guess that you won't be the only family unable to attend and a quick phone call to the school asking them to post out any paperwork would be adequate.