The female-Type-A legacy cable to male Type-C is a legal cable assembly, per spec. I think it is a misprint in the question.
However, adapting the new Type-C device plug to legacy Type-A host port is indeed a challenge, and it is not addressed by specifications. Although there are Type-A receptacle to Type-C plug adapter dongles (as referenced in the question), they cannot provide one of main benefit of Type-C connector, the universal polarity of it. The other problem is that the simple passive dongle will provide always-on VBUS, which is against Type-C mode of operation. Other than that, they should work if nicely implemented, you just would need to flip the Type-C connection in 50% cases to get USB 3 speeds, and the USB2 should always work.
The right way to connect a Type-C flash drive to a legacy Type-A host port is to use a proper hub, with legacy type (A or B) of connector upstream, and full-blown Type-C receptacles on downstream ports. Recently Genesys Logic announced such hub controller chip, GL3523S, as well as others like Microchip and Cypress, but at this time it is difficult to find any OEM products with these chips yet, only development boards are available. If you should find a finished OEM product of this kind, please post.