Agreed, Mazda USA released a statement that only 300 were available there:
However, the original publication of the 35th Anniversary launch said:
商品開発本部 主査の斎藤茂樹氏は、「求められたすべて人にお届けしたいので、数量限定にはしていません。まだロードスターに載っていない方も、すでに乗っている方も、ぜひ乗り換えていただきたいです」とコメント。
Which Google tells me means:
Shigeki Saito, Chief of Product Development Division, commented, “We don’t have a limited quantity because we want to deliver to everyone who wants it. We want those who don’t have a Roadster yet, and those who already have one, to switch over.”
And matches the fact they aren’t numbered within a series (or at least weren’t upon reveal):
So Japan get as many as they want, the USA get 300 and no one else gets one?