Many hardware stores such as Ace, Do-it-Best, True Value sell stainless steel metric sheet metal screws. I buy stainless metric screws at such stores quite frequently. They have them in the small parts bins. Just ask the clerk for help. Going to the big box stores is generally a waste of time when looking for metric fasteners.
As to filling holes don't bother using wood and resin there is a better way to do it. Just buy epoxy putty sticks. The kind that are round with one component part inside of the other. You cut off the amount you want and then knead the two components together. Best screw hole filling material around. It sets fairly quickly and is just the right hardness after curing for holding screw threads. I have been using it for many years and I have gone through a lot of it while repairing my Campster
trailer for patching fiberglass and rebuilding areas of the plywood floor where the old bolts had rotted wood around them from water leaks
. Wonderful stuff, it is a standard item in my repair kit for the trailer, boat, workshop and house.