My DD works for a homeless charity. They have a tiny paid staff - basically part-time wages for more than full time jobs! - and a few volunteers. My DD was originally a volunteer and got involved through a weekly event to provide food for homeless and low income people. That attracted quite a few volunteers. They had a charity shop too, which brought in volunteers - but also required quite a lot of volunteers, so it wasn't a very good source of recruitment for other work.
The learning curve from volunteer to full-time worker has been fast and steep, as the charity itself was developing and they were learning how to put the correct systems in place. Covid-19 has made it harder. (DD is responsible for ensuring that everything is Covid-19 safe, in addition to all her other jobs.) You will know how complex the work can be, not only with all the safeguarding and confidentiality issues, the need to know all the relevant legislation, the networking, and so on. There are also the complex needs of the service users and often their challenging behaviour. I am sure that you can think of many more issues which make the work far from simple.
What I am trying to say is that there is a limit to what you can ask volunteers to do. At DD's charity, they have managed to keep some volunteers during lock down, although the charity shop and public events like free meals were curtailed. They have development plans for all volunteers to help them develop skills and confidence (particularly useful for the volunteers who were formerly service users). However, the vast majority of the responsibility has to be shouldered by the staff. It's one thing to ask somebody to serve hot drinks or give a sleeping bag to a rough sleeper, but a lot to ask a volunteer to deal with complicated issues where lives can literally depend on your work. DD's charity has trained some volunteers to do some of the initial work but the responsibility rests on the shoulders of the staff. I am not sure that you will get many volunteers who want to take that on. It's a big responsibility, a lot of work and often involves wrestling with bureaucracy. Not everyone's cup of tea.
As you can't do public events, which attract attention, at the moment I think your best hope is online. Do you have your own Facebook page for your charity? DD's charity has many followers online, amazing people who support them and will help out if there's a dire emergency - doesn't happen often but they are there if needed. If you can get followers for your Facebook page, maybe you can recruit from there.
You are doing good work. Bless you and good luck.