There are many companies that use portable x-ray fluorescence or spectroscopic methods to do PMI. You can check the "Buyers' Guides" of NACE, ASM, or ASNT. If you are in an area with a large number of companies with similar needs, your telephone directory's Yellow Pages may be sufficient.
Before you start, however, make sure you understand the capabilities and the limitations of these techniques especially if you are interested in detecting elements with a low atomic number.
Good Luck!!