Asking the engineer for the original is like asking a pro photographer for the pictures. They will give prints, etc, but not the original. It would be like cutting him out of the loop of his work.

With that being said, An "ASM" file is an "assembly" file and may contain "Part" files from several different systems. Breaking down the assembly and getting at the original model, which could be several different formats from several different systems, could be a lot of work, and also present translation issues if the "assembler" doesnt have access to the original part creation software.. You may be asking the engineer to sit down and do several hours worth of work, to get you the part exported out.