You can use some washers, that need to add up to 5mm on either side.
M10 washers work fine.
Spacers are the way to go though.
If you are reusing the bolts BE VERY CAREFUL, they will be shorter, so will have less to bite into.
You can use same gen GSXR caliper bolts, they'r about $5/CAD per bolt. if you want stainless.
Its cheaper to get suzuki bolts rather than go to a parts store and buy stainless bolts.
You can always use black oxide hex cap screws, but they will rust in no time.
Also the GSXR bolts look better than the regular grade 8 stainless bolts
M10 fine pitch, i think its 1.25 pitch, I can confirm if you really need the specs.
1997 Ninja 250 - Kawi Green - Sold - 25k (now in bike heaven)
1997 GSXR 600 SRAD - BLUE 19K
1998 GSXR 600 SRAD - Flat Black, with road rash. - 81k - 'Kawizuki" - Done!
2000 CBR F4 - RED, 32k - Sold
2004 Kawasaki 636 - BLUE - Current
1998 GMC Jimmy - 4x4 - 286k