I've recounted this before, but a friend had same problem. He was having a substantial extension built (which has probably doubled the size of the house) and some relayout of the existing house done. 3 years ago when he first started talking to builders, he asked if he could do the electrical and plumbing himself, and the answer was 'no', or at least, he wasn't going to get anything knocked off the price. When he finally got a builder earlier this year, that had all changed. When he asked the same question, the builder jumped at the chance -- he said he knew he wouldn't be able to find an electrician or plumber which was going to be a real problem getting the extension completed. Anyway, my friend did all the plumbing and electrical including moving the boiler. The builder helped out by supplying core borers and other tools as and when needed -- I think he was really pleased he wasn't having to deal with plumbers and electricians.
Over the last 5 years, I've probably had some 5 or so jobs which I've tried to get tradesmen in to do. Every time, it's involved phoning some ~10 tradesmen. On 3 occations I actually managed to get someone round to look at the job. Only ever got one quote, and the work done really wasn't very good (not up to the standard I could do it, but done much faster). I DIY pretty much everything now -- trying to get tradesmen is a big waste of time.