I've found that zip ties can be used to attach just about any accessory to a bike that lacks the proper braze-ons or eyelets. Search the electrical section of your local big box home supply store for a large selection of sizes and shapes. If you use the heavy duty ones you can really crank on them with a pair of pliers to get them really tight. I learned to use lots of zip ties on my scuba gear where they are perfect because no corrosion. Instead of snipping off the end of the zip tie with wire cutters, slice it off with a sharp utility knife to make the cut neater and less sharp.
For example, to attach a fender to the underside of a front fork that lacks an attachment bolt, just drill 2 holes on each side of the fender where the fork blades are and then zip tie the fender to the underside of the fork with a zip tie around the top of each fork blade.