You might be able to get it directly from RA Tech Support, but they're going to want a good reason (and maybe a disclaimer, in writing) about why you want to use an obsolete firmware revision.
If you want this because you or your client isn't willing to update your RSLogix 500 software to support the current firmware, the answer is likely to be in the negative. This is especially true because the RSLogix 500 Micro Starter software, which supports the MicroLogix 1100 controllers, is free of charge.