I think all Tandy released for the MC-10 was a couple games packs and a 16K RAM expansion. Someone on the yahoo mailing list has probably ported more BASIC games to it in the last year than was ever released for it originally. I don't think anyone supported the machine.
There is a 128K RAM/ROM expansion someone recently did and they added several more BASIC commands. There's also a drivewire like program emcee server. You can find details here: http://tech.groups.yahoo.com/group/TRS80MC10Club/files/AtkSoft/