I don't think there is 1 - and if u wrote 1 u'd hav 2 pay a licensing fee in order 2 distribute it.
But, if u wanted 2 do it then I'd simply place both imported 3ds objects in the same hiarchy (under the same pivot). U could then save the entire hiarchy as a single object.
But, if u wanted 2 do it then I'd simply place both imported 3ds objects in the same hiarchy (under the same pivot). U could then save the entire hiarchy as a single object.