[Blade Raider]

Kikaider is probably the most successful Ishimori hero in the US that wasn't changed into something else (liker Power Rangers). Most every piece of major Kikaider fiction has been released in the US officially in one way or another.

The two 70's toku series are currently on (way overpriced) DVDs. The Hakaider movie also has a US DVD. The original manga is currently available digitally on Comixology and the Code 02 manga was released in paperback (currently out of print). The anime series and OVA was aired on Adult Swim (making it the most widely known) and has DVDs complete with English dub (Sadly now out of print).

Only pieces of fiction I can think of not to be released officially in the US in some form are crossovers. Reboot getting a US release is really not a surprise. If there's a surprise here, it's how quickly it's been licensed.