Are you wanting the large single bolts? ..think they are M12s..or the 4 smaller bolts for each mount?...I replaced the large single ones from Rimmers..They are available elsewhere singly and you can buy generic versions but without the inherent thread lock, Make sure you look for something like 12.9 spec. The OEM versions are a little long IMO.
For the smaller ones..I think they are M8s..I would definitely go for the non-OEM versions because then they won't have the slot down the side of the bolt which encourages rust. I used 40mm long ones with washers..40mm was too long..If i had to do it again I would use 25-30mm long bolts..actually machine screws coz they are threaded all the way ...and make sure those are at least 8.8 spec.
....and definitely NOT stainless steel for any of the bolts..they don't have the tensile strength.
I'm sure there is a How To about this which details the bolts/screws required....I think....