The CIH offer a distance learning course, and Anglia Ruskin offer day release courses. The jobs market is very competitive at the moment, but some social landlords will take on trainee housing officers and put them through the relevant course as part of the training role. You may find that another route in may be to apply for jobs in the customer services or enquiries team with social landlords, as this will give you experience of some of the types of queries that come in. Alternatively I have heard of people working in benefits departments and transferring accross as landlord can use this experience within their HO teams.
Best advice, be open minded and be prepared to try different routes in- I'm speaking with experience of being both qualified and expeienced in a housing team, but struggling to find a job at the moment myself!