Have you tried contacting glazing companies offering contract services? Also look at property maintenance companies, especially those that have big contracts for social housing.
Yes I have tried that but they do not seem to want to deal with a small one man outfit. Same problem when I quote for insurance work. I'm miles cheaper than the big boys but for some reason they think they will get a better job done if they use a large company. I quoted to fit a composite door in a ladies house for £700. One of the big DG companies that uses a mountain as its logo went in at £4000! Work that one out?