Housing providers
Housing associations, registered social landlords, housing providers, local councils, call them what you will - these are the people who have the properties you want to buy!
They all have to market their properties through their local HomeBuy agent, so that's always a good place to start. However, if you've already got links with a housing association, or you've heard about a development, seen some advertising, then there's nothing to stop you approaching the provider directly.
Most of the properties they'll have on their books are likely to be New Build HomeBuy (shared ownership) ones, and many of them will also have details of shared ownership resales too. If you're more interested in the First Time Buyers' Initiative or HomeBuy Direct shared equity schemes, you'll find them being offered by private housing developers rather than housing associations though.