Check out Crypt::Random, which will fetch you an arbitrary amount of random data. You may have to pack this into a number if you need a number.

In a pinch, yah I don't see any reason why you couldn't just take 8 8-bit numbers or 4 16-bit numbers or 2 32-bit numbers, shift appropriately, and add them together. I'm not sure what you mean by 64 random numbers, unless you mean 64 random numbers in the range of 0 .. 1, shifting each one 1 bit over and adding the next. That seems like it would be a little inefficient.