I'm not aware of any law that requires you to hire a professional inspector.

Put out signs and lockboxes for realtors.Cold call for a realtor or investor.Create a handyman or property preservation business.Become a notary, so you can close real estate transactions.Go to work for a courthouse data service, so you're looking at and recording the posted data for them.Work for an apartment complex leasing apartments or doing maintenance.Work for a property manager doing make ready.Do anything and everything in construction.Become a home inspector willing to work weekends.Work as a sales rep or helper for a builder.Probably all these positions could use someone that wants to work nights and weekends.   

Then they may see the units with their inspector and get actual leases, etc (after signing NDNC).What local agent(s) are you working with?

PMs, contractors, Inspectors, Realtors, etc).If you fit that profile feel free to connect with me.

Have a purchase agreement on my first duplex and wanted to know if I should trust the Inspector that my real-estate agent selects/ recommends or find a 3rd party one that might be more impartial.

So you're essentially saying the roofer has no negative consequences for his bad, the city inspector doesn't have an negative consequences...and you have to pay someone to fix this issue?

If any BP forum has recommendations for inspectors and lawyer that would be great! 

Looking to get an external inspector to take a look at a potential investment property.

@Avi Lah  that town needs a new sewer inspector.   

Just get a thorough inspection from a trusted inspector.