Who makes 9mm AR-15 Barrels?
But before you jump one me for asking this question...
I need a barrel that is .750 in daimeter throughout (standard HBAR muzzle diameter) unlike the RRA barrels which taper under the handguard.

I plan on keeping the barrel under 10" maybe 5" depending on the ballistics and then attaching a suppressor to the end of it. Any help? Thanks Medic17

You could go with a TROS tri lug barrel.  They are the same diameter for the full length of the barrel.  They are available in the EE under NFA items.  I have one of these myself and they are quite nice.  He makes 5" and 9.25" barrels.  The only thing is that they are not .750 in diameter, they are slightly larger so I just had a FSB reamed out to that dimension.

Of course you could have any of the barrel makers build you exactly what you want.

No I do not need a tri lug. But reconfiguring a tros barrel may work. I will have to look into it. Thanks