just a thought (albeit not a tested one), what if you tried a 1/4 inch by 20 self threading bolt? 1/4 inch is like 6.35mm (I think that bolt is a 6mm by 1.0). it would be like using an oversized bolt (not sure if that is available either). good luck
(you could also rethread the hole to 1/4 if you have a tap that short
)