Maybe the Reds haven't invested heavily in left-handers because they haven't needed to.
Blaine Howell (13th round) has a 1.35 ERA this year and is looking very good.
Mace Thurman (19th round) signed for above slot money and has already been promoted to A-ball after completely dominating at Billings.
Bryan Gardner (34th round) isn't exactly blowing people away, but he has a respectable 4.50 ERA and 18 strikeouts over 18 innings in the GCL.
Matt Fairel (35th round) just signed for above slot money, and we've yet to see what he can do.
David Torcise (47th round) has a 1.71 ERA and 1.10 WHIP over 21 innings this year.
Joe Krebs (14th round), who has 49 strikeouts in 40 innings this year, was drafted last year and is already in Sarasota.
Shea Snowden (16th round) has been the GCL Reds' best pitcher with a 1.50 ERA and 1.06 WHIP over 36 innings.
Jeremy Horst (21st round) has been amazing this year with a 1.00 WHIP and 96 strikeouts over 85.2 innings.
Lee Tabor was drafted two years ago in the 30th round and is already in Chattanooga.
Jamie Arneson was a 16th rounder, but he was paid like a 4th rounder, so I wouldn't count him as the Reds not investing in left-handers.
Tzu-Kai Chiu was signed as an amateur free agent (for second round money, iIrc) and has a 3.34 ERA and 1.13 WHIP over 56.2 professional innings.
Matteo Pizziconi was signed out of Italy last year and has given up only one earned run over 17.2 innings.
Luca Panerati, also out of Italy, has a 1.50 ERA and 1.00 WHIP over 12 innings.
Aguido Gonzalez was signed just last year and all he has done this year is throw 30 innings without giving up an earned run.