Chuck,
It's possible that it is a seasonal item. It's also possible you just weren't looking in the right place (they are fairly small boxes and they can be just shoved some places). I couldn't find anything online either to post a link to it. I know that at the Lowes off of I-40 on the west side of the city (on Charlotte Ave.) they are on the end of the aisle (toward the back of the store) with the PVC fittings. There should be a bunch of the riser flex adapters there of different sizes. There should be some other irrigation supplies there also including sprinkler heads and outdoor drains. As I recall, the Lowes item number should be the same regardless of the Lowes and the number helped me find them the first time...
Sorry I can't really help much other than that. There may be a more common name for them that would get you a better search online, but I don't know it if there is one.
