I need to decide upon a pair of bolts that will be used on my motorcycle to mount a pair of frame sliders. The already present frame sliders are installed with (supposingly???) 10.9 grade M10x1.25x70mm (silver colored) bolts with hex socket heads. These two have slightly bent heads due to previous owner minor motorcycle drops and are acting as engine mounts as well. These two are not the original Yamaha factory bolts and probably came with the aftermarket protective mushrooms. This specific bolt size is quite hard to find in my country (Greece) furthermore for stainless material. Would it be safe to replace these with A2 grade stainless??? If not what is the minimum standard that i should try to match??? Any suggestions on how to shop these in Greece-Europe will be much appreciated...
I wouldn't trust the bolts you currently have to be right for the job, and I would definitely not replace them with some bolts you found at the local hardware store, and you don't have to. You should start by finding out the Yamaha part number, googling "Yamaha [year] [model] engine mount bolts" should bring up all sorts of useful information.
Once you have the part number go online to virtually any parts store on the planet and order them. There's loads of them in the EU, you don't have to order them from a Greek site. eBay is actually a good source of spare parts as long as you buy from sellers with a good reputation, some parts shops have their own eBay stores.
Lastly, you could just contact a Yamaha dealer and tell them what you need. You'll pay a bit more but you'll get exactly the right part.
EDIT: The OP explained that the original part number is 91314-10040, but wants a longer one. Yamaha bolt part numbers have the size as the second part, 10040 means M10, 40mm, so 10070 would give you a 70mm bolt. Unfortunately there's no corresponding part number, so I would go with a M10 70mm 1.25 thread (if you're sure that's correct), marine grade steel with the head type you want (hex head probably). A google search again will help you here, and you can order from anywhere.