How do I find out the fuel consumption of the PT6A for a lightly loaded aircraft? The Fuel consumption of PT6 engines provided by manufacturers are as follows.

Cessna Caravan - Consumption ~47? GPH. At full load at ~160? Kn.
Quest Kodiak - Around 49 GPH at full load at ~170 Kn
Pilatus PC12 - Around 69 GPH at full load and cruise speed of ~250Kn

I was analyzing the fuel consumption levels, distance travelled and the impact of the engine, when only one or two passengers are travelling. I couldn't find any information on the internet about fuel consumption when the aircraft is just loaded with 400-600 pounds.
Any information or sources where i could find this information?
You need to obtain the specific fuel consumption (SFC) for the particular dash number of PT6 (scroll down to the bottom for the chart with the data). For example, the -67A turboshaft is down around .47 lb/hp/hr, close to piston engine territory, but most are between .5 and .6 lb/hp/hr.
So pick the dash number of engine applicable to the airplane you want to compare, note its SFC, and now all you have to do is calculate the HP required of a given aircraft at a given weight to cruise at a given speed, and that you should be able to interpolate from the airplane AFM/Operating Manual's cruise performance and power required chart data, working out the HP required to cruise at Speed X, and Weight Y.
Once you work out the required HP, and you know that engine's SFC, you're there.