The SI base unit is actually the kilogram (despite naming), a metric tonne is actually a megagram lol.

Anyhow, if the prefix-less naming matched the base unit, 10 kg would be a “decagram”. As it is, it’s 10,000× the base of the naming system, and theres no prefix on factors of 10 above 1000, so sadly there’s no way to name it neatly.

Edit: actually it looks the like the Greek for 10,000 is “myriad”, so it would be a myrigram. Dope!