Hi!
I generated a pre-launch TLE based on the published target orbit (450 km x 450 km from the PressKit) with the inclination of BlackSky Global-1 (97.48°, source: skyrocket.de - BlackSky Global) for a launch 
at the beginning of the window (2019-06-27T04:30:00Z) using sattools by @cgbsat.
ELECTRON
1 84003U 19178.18750000 .00000000 00000-0 50000-4 0 04
2 84003 97.4800 346.5340 0000001 0.0000 219.5621 15.38685052 00
Launch site including marine safety area (source: Public-viewing-restrictions-Make-It-Rain2.pdf):
Take it as a first guess (this is only the second time I’ve done this). 
Sincerely,
kerel / Fabian P. Schmidt
update: The launch will likely be at 2019-06-27T04:40:00 (source: RocketLab tweet), updated TLE (using launchtle from sattools (explanation post):
1 84003U 19178.19444444 .00000000 00000-0 50000-4 0 07
2 84003 97.4800 349.0408 0000001 0.0000 219.5621 15.38685052 03