I can't think what the size if off hand but a Passap (roughly standard) machine is about 6mm. So.... 8? Anyway the next size down, Most machines come in bulky (that would be th 9mm) Mid gauge Standard Fine
Hi Brian, the Brother KX350 is a 7mm machine. As far as I know, it is the only 7mm machine made. It won't be quite as easy to find tools for it, but it is possible. Check with Peter Smith at http://www.sewknit.ca/ He is high, but he is the one most likely to have some.
Justina, I have gotten extra 7mm tools for my machines from Sunny Choi, Hong Kong Knitting, on ebay. They are much less expensive then some places. I have also found some in other ebay auctions and buy it nows at ebay.