The issue with lack of avalability is not market size, but rather market share. The on road market is smaller in the USA, but Yokomo is not just an on road car manufacturer, they make off road and drift kits, both of which are popular.
Yokomo wants more market share in the USA, I have had direct conversations with them. The issue is A Main is not pushing, promoting, ordering and distributing according to their original agreement. At the moment they might be exploring the way the car is sold in the USA. A Main is not just a reseller, they are the north American Distributor, however they are not distributing the cars, just retailing.
Yokomo is ready to have pre-orders, products delivered in a timely fashion, new releases all stateside asap, however their NA distributor is not doing their due dillingence. Some might say it's market size, however I would argue it is market share. A large distributor is never going to worry much about getting a niche brand off the ground. To them, Yokomo is just another part number that provides marginal revenue that adds to their bottom line.
Now in the case of on-road, the market is driven more by entusiasts and small business owners like RC America, TQRCracing, Reflex/RSD, Gravity RC, awesomatixusa, bsr, EAM, Express, etc. Much like it is in the European and Asian Markets, the distribution of products is less centralized and provides for an easier flow of products to the market. If A Main or Yokomo opened up their distribution to other stores or to a distributor that wants or needs the brand to succeed, you would see an immediate growth in market share, lower prices (the Yoke is cheaper than the 6.2 right now) and parts available stateside ASAP.
Sorry for the rant. We want to stock Yokomo stuff, really bad.