Nonzero for integers

My problem is as follows. I am generating a random bitstring of size n, and need to iterate over the indices for which the random bit is 1. For example, if my random bitstring ends up being 00101, I want to retrieve [2, 4] (on which I will iterate over). The goal is to do so in the fastest way possible with Python/NumPy.

One of the fast methods is to use NumPy and do

bitstring = np.random.randint(2, size=(n,))
l = np.nonzero(bitstring)[0]

The advantage with np.non_zero is that it finds indices of bits set to 1 much faster than if one iterates (with a for loop) over each bit and checks if it is set to 1.

Now, NumPy can generate a random bitstring faster via np.random.bit_generator.randbits(n). The problem is that it returns it as an integer, on which I cannot use np.nonzero anymore. I saw that for integers one can get the count of bits set to 1 in an integer x by using x.bit_count(), however there is no function to get the indices where bits are set to 1. So currently, I have to resort to a slow for loop, hence losing the initial speedup given by np.random.bit_generator.randbits(n).

How would you do something similar to (and as fast as) np.non_zero, but on integers instead?

Thank you in advance for your suggestions!