you can simulate this by using time as a seed, and thus re-seed before each time you need to get a new number.
If this is a number generator of sorts you are making,
my suggestion is to take the system timestamp or PB's datestamp,
get the current high precision timer stamp, combine the numbers.
And you should have a pretty random seed there.
And if you really make a lot of numbers per millisecond even.
Add a temporary incremental counter into the mix,
stay away from any form of hashes. As there will be hash collisions indeed
if you plan to make millions of random numbers.
You could also do what some cryptology experts are experimeting with,
chaos and noise. Use soundcard and video input (webcam) or similar,
there will always be noise in the input, use the noise as the seed each time you wish to re-seed. (i.e before each number)
sound and video input has a lot of white noise, the computer is able to capture it.
That noise is actualy universal noise/interference (and general human electronics noise as well).
Warning!
If you do not wish to have the same number appear twice in a row etc.
(remember, random is truly random, so there is always a 50% chance the same number is picked again even if it was picked a moment ago)
If you want a unique list of random numbers with as few "repeats" as possible,
what you need is a pseudo-random generator.
Most research focuses on pseudo-random generators so you should not have to much issue finding examples,
maybe even assembler.
a good starting point is looking up pseudo-random in wikipedia
and then google a bit around.
http://en.wikipedia.org/wiki/Pseudo-random
