Are there any suitable alternatives to alcohol/brake cleaner for cleaning brake rotors? Alcohol and brake cleaner seems to be the recommended options for cleaning disc brake rotors. I don't have any of that available currently, so are there any suiltable alternatives to them that can be used safely?
The main question is why are they needing cleaning, as this drives the need for chemicals. 

If its normal road and trail mud and grime, as suggested in the comments, hot water and a nylon scrubbing pad (even a "goldilocks" type metal one if used gently). If you remove the wheels to be safe, then use a bit dish washing detergent and rinse well with hot water and dry off with a cloth. If you need a bit more "omph" the toothpaste is mildly abrasive and easily washes off afterwards. Try not to touch the rotor once cleaned.  

If you have oil contamination, and the above has not worked, you will need a solvent  - anything volatile that does not leave a residue should be OK as long as it does not get on the pads, bearings or or tires. White petrol is ideal.  However if there is oil on the pads they should be replaced.