As you are no doubt aware, baptism records for St. Peter and St Paul, Lavenham, from 1558, are available on Familysearch, though you would need to do some research to find out if there are any gaps which may explain why you can’t find what you are looking for.
Marriages and burials aren’t available until later on Familysearch, though Boyd’s have marriages from 1558.
It could be that your Risbys came from elsewhere around 1667 if that is the earliest mention of them you can find in Lavenham. Are there any other Risby families in Lavenham prior to 1667?