If all else fails play playgroup bingo, people to look out for-
the leader, generally, but not always smily, will nab you as soon as you get through the door - might be a contribution to pay for tea/coffee - generally less than a pound.
the established mum - has quite a few friends around, two children, one might be at preschool, more likely to seem cliquely as all their friends there too
The veteran, has been going for 10 years, have x children at school, their youngest is getting too old for toddler groups but the mother still clings onto their 'baby'
The SAHD a brave man who enters this world, but generally seen as one of the crowd now.
The grandparent - glad of a few hours entertainment for their dgc VERY IMPORTANT do not confuse with the veteran
The child minder - good to identify and watch incase you need childcare at any time for your pfb, from toddler groups I have spotted some whom I would happily employ and others I wouldn't go near.
Hope it goes well, report back later!