Few and far between
Definition 1 of 1
Pro Tip 1/3Rarity Emphasis
Use it when emphasizing how uncommon something is in a specific context. 
True acts of selflessness are few and far between these days.
Pro Tip 2/3Negative Implication
Often implies a sense of disappointment about the scarcity. 
Since the factory closed, decent job offers have been few and far between.
Pro Tip 3/3No Exact Frequency
Doesn't specify how rare, just that occurrences are not often. 
Celebrity sightings are few and far between in our small town.