Ah, interesting. Just in case you missed it from the links above, TTN did buy such MA-S block:
This starts with 0x70B3D57ED and does mention an OUI, but it’s not my cup of tea:
Details OUI 70:B3:D5:7E:D Company name The Things Network Foundation Border left 70:B3:D5:7E:D0:00 Border right 70:B3:D5:7E:DF:FF Block size 4,096 Assignment block size MA-S