fender u nuts best place to buy?

The last time I needed some I got them off of Amazon. You might be able to buy them through automotive shops or through Dorman Help even at Canadian Tire or NAPA. You used to see them in the bins but that is less common now. I did buy a set specifically for my fenders from Classic Industries because they came with proper bolts and had the nuts with the integral washers. You should be able to get them from National Moparts too.