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You won't find the same Metric sized bolts (or longer) at any home improvement source (14mm). You'll have trouble finding the same Metric sized bolts (or longer) at specialty sources.
You might check with McMASTER-CARR for the 14mm in a longer length.
You can also go to C5 Tech, click on search this forum (in the red banner) and use keywords "lowering c5" or similar for hundreds (thousands?) of past posts that have instructions, images and sizes of the various sized (SAE) bolts that some members used.
If you go cheap on this, you may suffer bolt failure. There's some past posts on that as well.
The 9/16" Gr. #8 is stronger and is a fuzz larger than stock but will still go through your stock bushings. I installed 8" (stock are 6") and you will get at least a 2" drop in the rear.