Here is a trick I use when I need to quickly weather wood or weather the cut ends of barn wood. Get a sheet of bare steel. Spray it with vinegar and keep it wet so it rusts really good, they while wet spread paper towels to soak up the moisture and residue. Let the towels dry. Reactivate the towel with a little sprayed moisture and rub into the wood. I learned this from an old time carpenter that did lots of repairs on cabins, etc. and did the trim work on a project we needed "instant weathering" on.
I took a quick look at google and found this method using steel wool and vinegar that works too.