you can use rand_bit_stream from ahdlLib or vsource from analogLib. with vsource its not actually random, you can define the pattern arbitrarily.
45 data The bit string. A string that contains a series of the four states, 1 0 m z.
46 rptstart=1 The starting bit when repeating. The data repeats from the specified bit to the end of the bit string. The parameter should be an integer from 1 to the length of the bit string.
47 rpttimes=0 The repeat times. The output will maitain the state of the last bit after the last repeat. If its value is negative, the string repeats forever.