Been loads of posts on this. O-rings from a hardware store (or online from RS and the like) are the cheapest bet if you feel you need them on your draws.
Though RS probably aren't the cheapest actually. Just look for any online o-ring supplier and order the size you think you'll need. They'll stretch about 20% safely before they risk tearing.
It's spring soon, I might just spend a few hours chasing lambs around the fields and chewing the rings off their tails. Always looking for ways to save a penny or two.
Podcast Factor Two - S2 Ep.3: Rick Allen - Clouds Come and Go
Press Release Arc'teryx Climb Academy returns to the Lake District: May 25th – 27th
Fri Night Vid Siurana - A Limestone Paradise
In this week's Friday Night Video, we follow Robbie Phillips and friends to Siurana, Catalunya, where he aims to regain some sport climbing fitness to tackle James Pearson's Le Voyage. It had been a decade since Robbie had been on a Spanish bolt...