What do you mean, "they just disappear"? Did you try to hire one? Perhaps they are very busy, or if you were vague about the work you want done they may have thought you were just price shopping.
First of all, I try to learn about the project and products so's I can ask intelligent questions...if you don't research, you are likely to be stiffed either in terms of product or workmanship. BE THERE every minute anyone is working on your home.
I like to get names from people I know who have had similar work done. If I can't do that, I find someone I know has been in biz for a serious length of time. You can probably get names, probably not recommendations, from suppliers who sell the siding or windows. Some mfg. co. have certification programs for contractors. Contact county or city licensing agency to see if they have license and any actions taken against their license.
You must have neighbors who have had same work done .. talk to them re products and contractors. When you know exactly what you want, then get bids specific about product brand/type, sizes, start/end, insurance, lien release. If you hire two contractors, they need to coordinate schedules and that should be in writing.
We had a bad roofing job done at our condo, before we moved in, and the contractor was working with us until one of the less pleasant board members got nasty with him. They should have sued him right away, but were too lazy..talked legal action after he had been back several times for major rework and ended up pissing him off. Sometimes being sued is more pleasant than working with a-------.