I say buy them from your bike shop locally.
Here's a tip I got shortly after I joined these forums and it works. In the box or plastic bag you carry your spare tube on your bike put a cotton ball in too. When you pull the bad tube out rub the cotton ball inside the tire and fibers will pull off anywhere there's a sharp.
A single serve wet wipe (I swipe them from BBQ joints) is nice in that package also for after you re-mount the tire.
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