I thought they did. It seems like a fairly simple gimmick for a toy to have.
I'd honestly be surprised if it didn't exist.

I can imagine Rod Form would look a little gammy.

Well, I think they'd all look a bit too bulky to accommodate having 4 forms for the armor, but I wouldn't imagine Bandai missing an opportunity for a Den-O figure like that.

Plus I assumed that's why the armour did what it did in the show, because of a toy.

Is it possible to retitle Gaim as "Nobunaga the Fruit?"

No.

I'm pretty sure they did. I think it was a Shouchaku Henshin.

Edit: No, I was thinking about this, which doesn't have the transforming armor: http://myfigurecollection.net/pictur...f=item%3A55809

I own that. It's cool

But yeah, can't find anything that transforms. Weird. Guess it was just a creative decision.

I know there was a Kiva figure that transformed into all four of his Arms Monster forms. It was laughably bulky.

Huh. Odd that they wouldn't make a toy using Den-O's transforming armor. I know it wouldn't be easy to design, but still...Odd.