Also do a search for 'canvassing' and 'leaflets' and read every post till around page 12. There'll be a lot of stuff not applicable to you; but read it anyway.
Another option maybe to buy a small round, work part time and canvass.
Unless the window cleaning is retiring or leaving window cleaning, he'll just be selling off his rubbish; generally.
Remember, lots of lads start window cleaning after reading some of the high-earning posts here; then find out that after X amount of months they can't make anything close to that amount, or just can't hack the regime.
A few years back I sold a little bit of work onto a lad with two kids and a steady job as the Celtic Manor Head Gardener.
He then bought a large round some distance from where he lived. He aimed to be earning 100,000 within two years. That's what he told me. He even had an 'employee' (of dubious status).
I met up with him one afternoon, about a month after he started. His eyes were glazed; he looked knackered; and remember this was a bloke used to physical out-door work.
He confided in me that he was struggling to make £50 per day.
I didn't ask, but guessed his family had been through a bit of turmoil; a loan maybe; and then he just packed it all in.
He managed to get his old job back at the Celtic Manor and somebody must've done well picking up his round.
Sorry to be negative; just realistic. During my first year I must've wanted to jack-it-all-in on a weekly basis.
It takes time to build up your speed, customer skills and gain a good and steady cash-flow.
My advice; boring and safe as it is; is to get a job to cover the bills and start window cleaning on a part time basis.