Evolved Ballistics has them in stock. I've never ordered from them but they seem to be legit.
Barnes .277 Cal 129 Grain LRX (50 Ct)
Barnes 277 Cal 129 Grain LRX | Barnes LRX bullets have been developed to match the advancements in rifle accuracy and extended-range optics. The LRX features a long profile and boattail design that delivers match-grade accuracy at long range with an incredibly high ballistic coefficient and...evolvedballistics.com