where can i get a good pair of new 10mm to 8mm cylinder/head studs the one that are 10mm in the cylinder and the step up to 8mm in the head

Go to your local Suzuki dealer and order head studs for 1990 LT 550, they are 10x1.25 on the cylinder end and 8x1.25 on the head end of the stud.

Have someone that has a mill and knows what they are doing, do the machine work.  The recess that needs to be machined for the flange on the 10mm end of the stud should only be a few thou. larger than the flange on the stud. 

We have not been able to o-ring some heads because the machinist that installed the 10/8mm studs, cut the flange holes too large and there was not a place for the o-ring to seal against.  The 0-rings are real close to these cutouts for the flange.