Your husband is perfectly able to join a housing association list. They'll factor your income into his application to determine your need-basis for a housing assocation home, but he's perfectly w/i his right to join a list. In some councils, such as Edinburgh, all housing associations use the same application, together with those applying for council housing. In other councils, like Glasgow, ALL 'social' housing is now handled by a housing association; there's no such thing as 'council' housing a/more as the ownership and control has all been given over to one or more housing associations.
Depending on the demand for affordable rented housing, shared ownership is being offered less and less in some areas, and can be close to non-existent in certain councils (Edinburgh, for example) where the average price of a two-bedroom 'home' far exceeds the average wage. This ensures that the stock of social housing will remain available for rent. In some councils, the right to buy has been suspended for a specified period or even indefinitely due to extreme shortage of affordable rent properties. It is possible to buy s/one's 'share' privately, but at full-market value, which puts it out of the range of most of those who are finding it hard to get on the property ladder. You may find such shared ownership properties for sale in your local property pages.
Waits can be VERY, VERY long for any susbsidised housing in urban areas such as London if you are not considered homeless or in exigent need, so don't give up and don't stop pursuing other options!
Hth.