Having enough randori partners is a common problem faced by an overwhelming majority of judokas around the world. Unless you live in a country like France or Brazil or Japan, you will have difficulty finding enough training partners.
The lack of randori partners is a problem almost everywhere because judo is a niche sport in most parts of the world.
I recall a German friend telling me about how some players have to travel three or four hours, to a big city, far away, in order to have good randori. They would drive there, have their randori, stay overnight and drive home the next day.
Based on my experience, if you want a certain number of people on the mat, you will need to have three times that number of members. So, assuming you want to have at least 20 people on the mat for a session, you will need to have at least 60 members because if you are dealing with working adults who do judo recreationally, you can expect to get only 1/3 of your members coming for training on any given day.
For someone who is not used to judo, only 1/3 may be a surprising figure but if you train regularly in judo, you will know this is true.
Working adults have busy lives, with many obligations and responsibilities. And all kinds of unforeseen circumstances crop up all the time. On any particular day, a person might be held up because they have to do something for the family. Or, they have to work overtime at the office. Or, their car broke down. Or, there's a farewell party at the office. Or, they fell sick. Or, they have to do some babysitting for a neighbor. Or (fill in the blanks). There are countless reasons why the other 2/3 cannot make it.
So, as a coach, if you want to regulary have 20 people on the mat for each session, you'd better build the membership up to 60 people. Then you won't have a problem with low attendance anymore.