I can’t play a full length C flute but wondered if anybody made a 5 or 6 key flute in the key of C and if it would match a C flute in sound. I already am learning the 6 key Bflat marching flute but would like to play along with my daughter sometimes. She has a C keyed flute. I can’t transpose my Bflat to the scale of key as I have Chronic Fatigue syndrome and it has made me dyslexic and other stuff. 
You’re talking about a high C instrument, right? That would usually be called a piccolo or fife. Hammy Hamilton could make you a 6 key C piccolo. Other than that, I don’t know of many options. Skip Healy makes a nice keyless C fife, and is looking to see if there is interest in a keyed version of his piccolos, so you might try there. Keyless from either of these 2 makers will run you over 300 Euro, though, so just imagine how much more it will be for a keyed version.
For a lot less money, keyless C fifes are available from Cooperman Fife and Drum and from Sweetheart Flute Co. And for the best bargain around, Tony Dixon has the C whistle with a flute head. You can cross finger or half-hole the accidentals on any of these instruments. Builds dexterity. And character.
I hope this has been helpful. Good luck!
Thanks. I already have the Tony Dixon C head and like that. I just wanted a small flute with keys in the same key (C) as my daughters long one.