Caffeine reduction in tea
You might look for certain seasonal varieties. I've read the tea with the highest caffeine content is late spring and summer harvests. Autumn tea is said to have naturally less caffeine, but certainly not none. I've had some autumn Darjeelings that are wonderful. There are some winter harvest teas, which might have even less caffeine than autumn teas. See for example Taiwan Sourcing,
@Webley - Which type of tea?
I ask because some cultivars and terroirs are more stimulating than others, and I believe not all of the stimulating factors are from caffeine. Avoiding these will help a great deal.
Lastly, I have wanted to try to remove caffeine from tea using liquified carbon dioxide but have too many projects to take on another.