If a system has a defective compressor, finding a replacement is generally easy: Find the local wholesaler that handles the brand you need, give them the model number of the original compressor, and they sell you the same model compressor.
Occasionally, the original compressor model is not available, and you will need to cross it over to a replacement. Generally, the wholesaler does this for you, but since you are ultimately responsible for its installation and the operation of the system, you should verify the right compressor is being used.