What exactly do you want to know? There are definitely de Rosa MTBs out there. I have seen one too.
Casati, Ciöcc, Pinarello, Cinelli, Pesenti, Basso etc. They all made MTBs.
Its very hard to get any decent information on all those mysterious Bikes.
I`m looking for a fork like this.
It should definately have chrome blades, 1 1/8" diameter, and in the best case it has a 17cm long threaded shaft.
I would be happy if someone offers me one.
I also had one of those pink Sentieros. And a blue Sentiero with little Animals painted on. I sold both. The pink one was too big and the colour was bleached. I really really regret selling the blue one.
Whats nice about Cinelli is that they put Cinelli Bars and Stems also on their low models...