According to the Zombie Heaven liner notes and Russo's Collector's Guide, fifty years ago to-day (23 October 1967), the Zombies' "Friends of Mine" b/w "Beechwood Park" (CBS 2690) was released. It was the first single from the yet-to-be-released Odessey and Oracle.
The Zombie Heaven liner notes actually list two contradicting dates. 23 October is the date given in the discography, but the chronology lists 22 September. I think part of the confusion here is that these two dates are also when Paul Atkinson was engaged (22 September) and married (23 October) to Molly Molloy.