RPM makes just about every variant of the FT-17 WW1 French light tank. It has a US version as well as a Japanese version, captured German, etc. They do them both in 1/35 and 1/72.
Tauro makes the WW1 German A7V heavy tank and the Fiat 3000 (Italian copy of the FT-17).
Emhar's line includes the Mk IV Male, Mk IV Female, Whippet, Mk IV Tadpole and I believe they are making a Mk IV Hermaphrodite. In 1/72 scale they do the Mk IV Male, Female, Whippet and A7V heavy tank.
Matchbox does the Char B and FT-17 in 1/76 scale too.
Not a whole lot of early armor kits out there, but then again, there weren't a whole lot of actual early armor vehicles.