Here are bolts grade 12.9 just as per BMW spec. One is m8x35 and the other M10x75. That is where I ordered mines from.
Here choose M8x35:
https://www.ebay.co.uk/itm/M8-Cap-Head-Socket-Screw-Allen-Bolt-Steel-Grade-12-9-Zinc-Plated-DIN912-8MM-8mm/153751968023?ssPageName=STRK%3AMEBIDX%3AIT&var=453773573693&_trksid=p2060353.m2749.l2649
Here, choose M10x75:
https://www.ebay.co.uk/itm/M10-Cap-Head-Socket-Screw-Allen-Bolt-Steel-Gr12-9-Zinc-Plated-DIN912-10MM-10mm/153764201293?ssPageName=STRK%3AMEBIDX%3AIT&var=453786732743&_trksid=p2060353.m2749.l2649
Thanks for that - I've ordered some too