I think you need to describe exactly what you have in mind.
There are various bits of kit described as Baldric belts. Some are just a long belt double wrapped one loop high the other low with a sheath where they cross over. Another one is just a belt worn diagonally across the chest with a sheath/scabbard hanging at its lowest point. The third, that I know about, is the same as the latter but with a belt around the waist that stops the diagonal strap/belt swinging around. The diagonal strap take the blade (or gun) weight, the waist belt stabilises it.
You could make a decent Baldric style belt of the third kind with two leather belts (one quite long), a sheath, and join the two belts together with rivets or riveted rings and clips. I would cut the shoulder strap to make a neater junction. Obviously, you also need a sheath - I would put that between where the two ends of the shoulder strap join the waist belt.
Making leather belts from scratch is quite straight forward. You can even buy the belt strip pre-cut from leather suppliers who will also be able to supply all the buckles and clips you need. Ideally, you would sew it but rivetted belts are perfectly acceptable, easier to make, and you don't need to buy a load of gear to do it.
