Hi - you will find that most people already have someone to do keyholding and cleaning - lots of people do this to supplement their pensions or other part-time incomes and they will do it for very little payment. You will eventually get work through personal contacts - ie neighbours and word of mouth, but so many people around here are desperate for money that you will find lots of competition.
You could try the rental agencies in the area and this is probably a good time of year to start asking around and leaving your details. The rental scene won't pick up until Easter and many of the agencies get rid of most of their cleaners during the winter so they may be happy to take your details for later in the season.
I would imagine that most builders use Spanish companies to do their initial cleaning but there are very few new builds being completed around here at the moment so not much work there, I'm afraid. There are some new developments which should be finished later in the year at Los Dolces and La Rioja but, as I said, I think that work will go to Spanish companies.
You have moved to a great area but finding work is the hardest thing about living here. Good luck!!